ARMY MEDICAL LIBRARY WASHINGTON Founded 1836 hvwieA Section Number CDay^fAry ...... Fobm 113c, W. D., S. G. O. ire 3—10543 (Revised June 13, 1936) DUE TWO WEEKS FROM LAST DATE I OCT I 1061 GPO 881473 * JVoJ/r^'-< *V REGISTER PAPERS: A COLLECTION OF CHEMICAL ESSAYS IN REFERENCE TO DENTAL SURGERY. BY GEORGE WATT, M.D., D.D.S., PROFESSOR OF PATHOLOGY AND THERAPEUTICS, LATE PROFESSOR OP CHEMISTRY AND METALLURGY IN THE OHIO COLLEGE OP DENTAL SURGERY, ETC. ETC. PHILADELPHIA: PUBLISHED BY S. S. WHITE. 1868. ye/v/3 ca ^ 4 <^ *J V \ o\ V o- ^ \' V V Entered, according to Act of Congress, in the year 1867, by S. S. WHITE, In the Clerk's Office of the District Court of the United States for the Eastern District of Pennsylvania. Lippincott's Press, philadelphia. TO MRS. SARAH JANE WATT, TO WHOSE SYMPATHY AND CO-OPERATION ITS PRODUCTION IS MAINLY DUE, m$ tittle WoXmt IS AFFECTIONATELY INSCRIBED BY THE AUTHOR. (hi) PREFACE. The essays contained in this volume were writ- ten for publication in the Dental Register, with- out a thought of their appearing in any other form. Both by private letter and personal interview, the author is very frequently asked for detailed statements of his views on subjects more or less fully discussed in these papers. Having neither the time nor strength to comply with the solicita- tions thus made, nor to answer the various ques- tions propounded to him, as satisfactorily, to him- self or others, as many of them are answered in these essays, he has been induced, in accordance with the advice of many of his best friends, to offer them to the public in this form. With the hope that they may do something to advance the worthy cause for which we all labor, they are respectfully submitted. 1* (v) CONTENTS. PAGE Preface .......... 5 Lord Oxygen ......... 9 Lady Hydrogen ......... 20 Dental Chemistry—an Introductory ..... 30 Thoughts on Dental Caries ....... 39 " But one kind of Dental Caries" ..... 45 Dental Chemistry of the Mouth ...... 48 The Action of Topical Remedies.....71 Cold Applications to Aching Teeth . . . . . .88 Intrastomatic Galvanism ....... 91 Alveolar Hemorrhage........97 Nitrate of Silver........101 Arsenic and its Compounds.......104 Exposed Pulps—Secondary Dentine.....109 Bleaching .......... 116 Calcium and its Compounds......118 Chlorine..........131 Spirit Lamp Explosions.......141 The Amalgam Question.......144 " Argentine" ......... 167 Smells and their Management......171 Professional Signs and Advertisements . . . .181 Theoro-Practical Hints........183 Alloys..........186 " Soluble Quartz".........192 Alloying Gold.........195 (vii) viii CONTENTS. PAGE Management of Gold Alloys.......200 The Cold-welding Question......209 Painless Surgery ......••• 211 Reply of the Graduating Class......213 Facial Neuralgia....... .217 The Dental Profession and its Appropriate Work . . 220 Random Thoughts........233 Professional Longings ....... 237 Fistulous Opening through the Cheek.....243 Nitrous Oxyd as an Anesthetic......245 " Teeth Extracted without Pain"......252 CHEMICAL ESSAYS. LORD OXYGEN. From an Introductory- to a Course of Lectures on Chemistry, I860. Man is, to a great extent, a creature of habit. He dis- likes sudden changes. The schoolboy lingering on the bank, shrinking from the sudden plunge into the cold stream, demonstrates this truth to himself, while the pallid cheek and compressed lips of the commander about to order a charge, demonstrate the same truth to others. A disposition to hesitate precedes all great undertakings; and this is the great cause of that procrastination, known as "the thief of time," which, manifesting itself mainly in reference to repentance and matrimony, peoples this world with old bachelors and the next with reprobates. About to engage in a great undertaking, shall we not be allowed to indulge in the luxuries of this universal law of laziness ? About to embark for a four months' voyage, on the deep sea of an abstruse science, with imperfect charts, and in- experienced sailors, is it any wonder we incline to linger in port, and while away an hour, in view of the long toil before us? Let us, then, prove ourselves members of the great human family of procrastinatorS, by spending this hour, with less of toil and mental labor than will fall to our lot in the hours which are to succeed it. But man is also a creature of instinct. He can be (9) 10 CHEMICAL ESSAYS. taught to know and do many things; but some things he will, and from his very nature, must know and do without any teaching, and even in spite of instruction to the con- trary. He eats when he is hungry, drinks when he is thirsty, seeks for warmth when he is cold, and for a cool place when he is hot, not because his reason teaches him to do so, but simply in obedience to the instincts of his nature. Another, and one of his strongest instincts, im- pels him to worship that which he regards as worshipful. This instinct affords him no guide at all as to what he should worship. To do this, is the province of reason and revelation. And while these infallibly point out the great Creator of all as the only fit object of worship, in the highest sense of the term, yet there is a sense in which "gods many, and lords many," may and should be wor- shiped (or honored) with true devotion. But even here, reason and revelation must be his guide, or he will sink to the folly and crime of gross idolatry. All worship, even in this subordinate sense, should be consistent. Consistent idolatry is far less odious than that which is inconsistent. We might pardon the astronomer for his worship of the stars; but we would be disgusted with his homage to a golden calf. Every man should be engaged in a good cause, and should admire, honor, or worship it accordingly. Being now about to engage in the study of an import- ant science, let us ask ourselves if the cause is not a good one. And if good, shall we not honor ourselves by honor- ing it ? As the youth seeks the society of her whom he adores, so let us manifest our love for this science, by seeking an intimate acquaintance with its truths. But if you doubMhe propriety of rendering homage to this science, and fear that in doing reverence to it, in all its ramifications, we maybe regarded as "too supersti- tious," let us turn our attention to a single element which LORD OXYGEN. 11 it reveals to us, and inquire to what extent, if at all, it is entitled to our admiration. What, then, is the character of oxygen ? To what ex- tent is it entitled to our consideration ? How much respect do we owe it ? What reverence must we pay it ? Shall we worship it ? Man naturally admires and reverences that which is mysterious. And this element is invisible. It is seen only in its works, which are many and wonderful. It forms the ocean and the land. It presides over the atmos- phere, and governs the changes which take place on the earth's surface. The other elements are its servants, and are forced to aid in its manifold labors. With one it forms the raindrop and the dew; with another, the balmy atmos- phere ; with a third, the flinty rock; and with a fourth, the miry clay. With one it fans the genial fire, and with another extinguishes the destroying conflagration. These are but parts of its ways—ever busy, but still invisible. Nor is this all of its mystery. Where is it? Nay, where is it not? Is it omnipresent? It extends high above the mountain crag, and far below the ocean's bot- tom. It accompanies, or rather carries, the eagle in his most daring flight, and follows the miner down deep into the bowels of the earth, and is there even before him. It rides on the swift wings of the wind, and rejoices in the storm-cloud; for both are creatures of its construction. It is in the middle of the mountain, in the solid rock, and in all things that live. Man cannot define its boundaries. To him it is, practically, omnipresent. But think of its power. In the morning of creation it combined with the lightest and least tangible of all its comrades, and formed the fountains,, rivers, seas, and oceans. In like manner, by other combinations, it made the solid earth. It seized a bright metal and turned it to lime. It laid hold on the diamond and changed it to a 12 CHEMICAL ESSAYS. gas. Forcing these to unite, it formed the solid marble. It raised itself on the wings of the wind and became the vital principle of the atmosphere. And having formed the seas, the dry land, and the air, it presided over and took part in the formation of plants and animals to beau- tify and people the earth. And ever since it has been busy, and still it is powerful. It organizes the forces of its kindred elements, and works wonders at which man stands aghast. We behold the majestic steamer, stem- ming the river's current or riding on the angry waves, defying the wrath of the mighty deep, mocking at wind and tide, and reaching in safety its destined port, and all through the agency of this grand and glorious element. The ocean having spread itself out as a barrier to the progress of man, this hero element comes to the rescue. Taking his favorite partner, the delicate Hydrogen, he goes into the very heart of the mighty engine, and to- gether they form its life-blood. He calls for his servant Carbon, and fans him into a flame, imparting warmth, and life, and motion to the mighty machine of his own build- ing; and the ocean is subdued, the winds are overcome, places far distant are brought nigh together, man becomes ubiquitous, and all are neighbors. With the same mighty machine he drags the lightning train across the land, over iron bars of his own forging, laughing at distance and mocking at time. His lightning train over his iron track ! Nay, it is thus he travels, at leisure. When pressed for time, he calls down the lightnings of heaven, and sends them forth across land and sea, on the wiry track which he has prepared for their guidance. May we not well exclaim, O Oxygen, great and marvelous are thy works ! But our hero element is powerful to destroy as well as to build up. Few, if any, elements have hardened them- selves against him, and have prospered. The strength of iron is as nothing with him, and weapons of steel he LORD OXYGEN. 13 grinds to powder. Gold becomes as fine dust Lefore him, and silver as the blackness of darkness. He calls for the aid of his servant nitrogen, and the solid marble melts like snow. Helped by another servant, the flinty rock becomes grass and stubble before him. The leaves wither at his blighting touch, and nature is dissolved by his blast- ing energies. Let us think, for a moment, of the ruin he has wrought since creation's morn. The flowers, the trees, the birds and the beasts of ancient days have all been swept away by the hand of this ruthless destroyer. He has swept over the earth, and nations have withered by the blast of his breath. Great Babylon is fallen—is fallen, and by his mighty hand. Where are the cities of the old world ? He has burned them to ashes, or crumbled them to dust; and over their ruins he raises the shout of tri- umph, and rushes forward to new conquests. When the whole world had rebelled, he destroyed it by a flood—all its inhabitants, save one righteous family, which he car- ried in his bosom, and wafted, by the genial gales of his balmy breath, to a place of safety. He has broken the ships of Tarshish with his east wind. He has over- whelmed fleets and navies in the mighty deep. Great is the ruin he has wrought, and still he is unsatiated. He forges the thunderbolts of war, and gives to them their destructive energy. He manufactures a cooling salt, which, in the hand of two of his servants, becomes a demon of destruction, hurling forth "firebrands, arrows, and death," and imitating the thunders of heaven. Nothing material escapes his destroying hand. He devours the widow's bread, and wastes the fruits of the earth, to create the demon alcohol, that the world may be filled with crime, and men may be changed to devils. He is the merciless executor of that sentence, "Dust thou art, and unto dust shalt thou return." And then just think of his petty annoyances. While he 2 14 CHEMICAL ESSAYS. blows the smith's fire, he consumes his coals, and wastes his iron. The surgeon rejoices in his shining blade, and the dentist delights in the lustre of his forceps, but he watches for their negligence and covers them with rust. He withers the leaves of the lady's arbor, and sours the milk in the dairymaid's pans. No annoyance is so petty that he will not stoop to it. He addles the egg of the patient bird, and moulds the food of the busy ant. He breathes into the pantry, and the bread becomes stale, the butter rancid, the meal musty, and the meat tainted. He rots the farmer's fruits, his farm-houses and fences, and turns the housewife's jellies and jams to vinegar. In short, he is prying, petulant, and impertinent. Shall we reverence such an object as this ? Shall we even respect it ? Nay, shall we not ignore or despise the science that discovers it and reveals its attributes ? But why should we not reverence it? Why not even worship it? While sages sacrifice to devils, and savages worship the storm-king, shall we fail to worship oxygen ? What if it is the great destroyer of our race ? Should we not try to propitiate that which will one day crumble us to dust? But let us turn from this and think of his goodness. Why, he blesses us every hour—gives us a new blessing with every breath! But how shall we specify his acts of kindness when we owe him our life, and are each moment dependent on him for its continuance? In the earliest moments of our helpless infancy, he breathed into our nostrils the breath of life, and has breathed new life ever since. He allays our hunger, and quenches our thirst, with food and drink adapted to our appetites and desires. He not only surrounds us with good things, but he is so jealous of our welfare that he rushes into and explores every avenue of our bodies, lest there may be something there to harm us. He ransacks our entire systems—veins, LORD OXYGEN. 15 arteries, capillaries, and cavities—and comes out loaded with poison twenty times a minute. He makes every pore of the skin an outlet for the purification of our bodies. He kindles a fire to warm us when we are cold, and fans us with the cooling breeze when we are hot. He builds us houses, like palaces, to dwell in, for our comfort and protection. It would seem as if he were determined that man should live always—not only live, but that he should riot in all the imaginary luxuries of a fabled dream. Not content that man should live—that he should breathe the balmy air of a life-giving atmosphere, that he should slake his thirst from the sparkling spring, and eat of that which is good, and delight his soul in fatness— our favorite element overwhelms him with delights, of which he could not even dream, were they not constantly showered upon him as happifying realities. How he blesses our sight! He clothes the earth with its carpet of green, and covers the forests with the same gay colors. "Gay green ! thou smiling nature's universal robe!" And our hero is the dyer that colors that robe. He paints the flowers with their varied hues, he screens the sunset with its crimson veil, and curtains the heavens with the fleecy cloud. And think of his beauty as he glistens in the dew-drops, and sparkles in the rain, or when he spreads the canvas of the storm-cloud, and illuminates his face with the day-god's pencilings, in the hues of the bow of promise. He moistens the eye of the maiden till it glistens with love. He fans her cheek till it rivals the rose, and bleaches her brow to the lily's hue. And even when he appears to frown—when the face of nature is wrapt in decay—he makes her beautiful even in death. When the forest leaves fade—as fade they must, for they are mortal—he beautifies their death-robes with his varied tints, till the eye is entranced with the gorgeous colors, 16 CHEMICAL ESSAYS. and even the south wind accepts them as substitutes, and no longer "Searches for the flowers Whose fragrance late he bore, And sighs to find them in the wood And by the streams no more." But not only does he delight the eye, but he charms us with the melody of nature. He teaches the bee to hum, the bird to warble, and the child to laugh. He gives voice to the singer, and tones to the lute and organ. In short, he blesses us through all our senses. Nor is he at all capricious in the bestowal of his favors. In spring-time, he moistens the earth with showers, fans it with gentle breezes, and bedecks it with flowers. He makes the grass for the cattle, and the tender herb for the service of man. In summer, he comes riding on the south wind, and warms and fertilizes the earth. He loads the trees with fruit, and causes the grain to grow for the sustenance of man and beast. In autumn, he blesses us with the fruits of the earth, and satisfies us with the in- crease of the ground, The harvest of the earth is ripened by his breath, and the husbandman rejoices in the abund- ance of his blessings. In winter, he converts even the fierce north wind into a blessing. He scatters hoar-frost like ashes, or spreads it, in silvery beauty, over the win- dow of the sleeper. He covers the earth with snow, and makes us rejoice in the tinkle of the sleigh-bell. At all times and seasons he is the same kind benefactor. He disburses his favors not only with a liberal hand, but without partiality. His goodness reaches to all men. Every department of life is blessed by his presence, and aided by his energies. He rewards the labors of the farmer with abundant crops. He brings merchandise from afar, over sea and land, to enrich the trader. He blows the fire for the smith, and turns the mill-wheel and LORD OXYGEN. 17 the spindle. He refines the ores of the metallurgist, and melts the founder's metals. To the physician and the dentist he is indispensable. He prepares the medicines of the one, and purifies the metals used by the other. No department of life is beneath his notice. He toils in the kitchen as a faithful servant, preparing and baking the bread, roasting the meat, browning, the coffee, and in- fusing the tea. He covers our tables with luxuries, and respects the appetites of the most whimsical. He fills the sails of the mariner, and wafts him to his destined port. He floats the schoolboy's tiny boat, and carries aloft his paper kite. He furnishes the painter his colors, and the sculptor his clay and marble. He carries the bird in its rapid flight, and goes deep down into the dark ocean, to bless the great whale and the little fish. He stops at nothing in his errands of mercy. Floods cannot drown him, and fire is but a plaything of his own creation. Height and depth are alike to him, and distance is only his delight. If not revered for his wonderful works, should he not be praised for his goodness ? Here, then, is presented to our consideration an agent, invisible, diffused, mysterious, powerful for good and pow- erful for evil; that goes about doing good, and, at the same time, seeking what he may destroy; that kills and makes alive; that wounds and heals ; whose existence ante- dates the life of man; which is indestructible as well as unchangeable. However we may estimate it, one thing is certain, that if it had been revealed by our science in ancient days, the great Jupiter would have been deposed to at least secondary rank. Had it been known at Athens, the apostle would not have found an altar "to the unknown God," but to the god Oxygen. And when we reflect on the characters of the gods they worshiped, we are led to pity their ignorance of this wonderful agent, which seems so much more worthy of the homage of their philosophers. 2* IS CHEMICAL ESSAYS. But while we pity, let us inquire if our worship of this would be found more exalted and purifying than their worship of beasts and reptiles, or wood and stone. What, then, is oxygen? Certainly it is a wonderful thing; for a wonderful God has created it. And because it is a creature, and not a creator, it stands on a level with its kindred elements—on a level with birds, and beasts, and reptiles, and is no more wonderful than they. In the light of our science, everything that God has made is wonderful, and, to us, incomprehensible. Everything is worthy of our admiration; and it is highly proper that the science we are about to study, which has a more ex- tensive range, and reveals more of the mysteries of the material universe than any other you are called upon to investigate, should teach us to "look through nature up to nature's God ;" to see the Creator in all his works; to look upon all the elements as but so many passive instruments in his hand. Till we are able to do this, we have failed to learn the great lesson taught by our science. But, gentlemen, do you expect to master the science of chemistry in the few short months we are to spend to- gether? As well might the traveler expect to traverse the entire globe in a single day, and return at nightfall to sleep in his cottage. No man on earth will ever get through with the study of this science. But shall we despair on this account ? May it not be "That one of the joys of our heaven shall be" a fuller and clearer knowledge of the chemical properties of God's universe than it is possible for us to have here ? But you may expect to obtain, by attention and study, such knowledge of it as will make all future study of it a pleasure, and a source of satisfaction. Are you discouraged and ready to turn back, on finding LORD OXYGEN. 19 that you make so little progress in this science? You have the same cause for discouragement elsewhere; for you have not and never will have a perfect knowledge of any science; nor would you be happy if you had. Here we know only in part; but there—we shall know, even as we are known. LADY HYDROGEN. An Introductory to a Course of Lectures on Chemistry in the Ohio College of Dental Surgery, 18Q6. "Which of you, intending to build a tower, sitteth not down first, and counteth the cost?" About attempting to build the superstructure of pro- fessional character on the foundation of professional at- tainments, may we not spend this hour in counting the cost ? A high tower we propose to build; and great in proportion will be the cost. And he who is not willing to incur the necessary expense, had best not attempt the superstructure; for only failure will result, " and all that behold it will begin to mock him, saying, this man began to build, and was not able to finish." In view of the magnitude of the science to which I am expected to introduce you; in view of the great depths of ignorance into which we are all fallen; in view of the great heights to which we must climb to gain even a Pisgah view of the promised land of science; in view of the fact that my efforts to guide you will be far too much like the blind leading the blind ; in view of the days and nights of mental toil and study in the months before us, it would be but human nature to spend this, the first hour of our acquaintance, in relaxation, if not in absolute rest. But shall we so spend it? Shall we not rather, with the aim of moving "immediately on the works," devote it to a review of our forces, and an inspection of the work that is before us ? (20) LADY HYDROGEN. 21 But the scope of that science to which we are assigned is too vast for immediate consideration—too expansive for the survey of a single hour. It extends down to the foundations of the earth, and reaches up to heaven. It includes all of earth, and air, and water, and meteors, and planets, and satellites, and comets, and stars, and suns. All material substances are subject to its laws; and the study of them is but the study of it. Shall we, then, abandon the building of the intended tower ? Having put our hands to the plow, shall we look back ? As soldiers marching against the battlements of ignorance, shall we desert our colors ? No ! but let us inure ourselves to the war by a gentle skirmish, before the grand battle begins. Let us spend this hour in the way of introducing ourselves to each other, and to our work. Like children "playing school," let us merely "make believe" that this is a lecture and you are students. Then, of all the material universe, let us select, for pres- ent consideration, just one element. And, that our labor may not appear heavy, let us take that one which is the lightest and least tangible,—the pliant, volatile, invisible, combustible little hydrogen. Hydrogen ! what inquiries crowd upon us with the very name ! What is it ? Where is it found ? What is it like ? What is it good for ? And a score of others. Patience, my friends. Let us consider. Far away back in the long-ago, before " the morning- stars sang together," " or ever were formed the earth and the world," in the distant past, when " He spake and it was done," God said, "Let there be" and "there was" an element, which from the regal character bestowed on it by its Creator, not inaptly has been called " Lord Oxy- gen." And because it was not good for this lordly ele- ment to be alone, his Creator saw fit to provide " a help- meet for him," and the beautiful hydrogen sprang up by 22 CHEMICAL ESSAYS. his side, and their marriage was sealed by the lightning's flash, and announced by the thunder's roar; and, accord- ingly, we are told, in the family record of creation, that "darkness was upon the face of the deep, and the Spirit of God moved upon the face of the waters." Ye who worship at the shrine of antiquity, and bow in reverence to " first families," here is something worthy of your de- votions. Here is the first recorded instance of definite chemical combination—the first marriage of elements. And so true have they been to each other, so close the tie of affection, so perfect the union, that for thousands of years they were regarded by the whole human race as "no more twain, but one" element. What, then, is hydrogen ? It is the lightest and most ethereal of all known substances. Too light to float the gossamer, or sustain the play of the zephyr's wing, too rare for the breath of the tiny insect, too diffused to carry the rose's perfume—a wonderful something which you can neither see, hear, feel, taste, or smell. But where is it? Or, a simpler question, where is it not ? It is above us, beneath us, around us, in us, of us. Go ask the forests the secrets of their growth, and they will tell you they have been watered and nurtured by the good Lady Hydrogen. Ask the flowers the source of their fragrance, and they will report it as a goodly present from the bride of Lord Oxygen. Admire their brilliant hues, and they will refer them to the artist hand of the same benefactress. Gaze at the rainbow, and you see but her pencilings. See her as she sparkles in the dew-drop, glitters in the rain, or glistens in the icicle. Admire her gentleness and purity, as she descends in the snowflake. Behold her majesty and grandeur, when the ocean is lashed to madness by the fury of the storm. Look at her stateliness in the floating iceberg, at her beauty in the shining frost crystal, at her tenderness in the falling tear. LADY HYDROGEN. 23 . Explore the wildest, deepest, most remote recesses of / nature, and you will find her in advance of you, beautify- / ing, building up, and sustaining. Everything that lives is sustained by her, and, deprived of her genial presence, would pine and die. And though practically almost omni- present, yet she is never impertinent—never intrudes— neither meddles nor gossips. By her quiet presence, she manifests her willingness to serve those who need her • sympathies. Though true to her first love, and faithful to I her marriage vows, yet she willingly co-operates with the humblest member of the family of elements, if so she can be useful. Indeed, so modest and retiring is she, that her i presence is not suspected, even by those she blesses. "Many daughters have done virtuously," but she excels them all. Such brilliance, and gentleness, and purity, and grandeur, and tenderness, and beauty, may well claim our attention and admiration for this hour. Shall we \ grow sentimental over the historic beauty of Helen, or : ecstatic before the image of Venus, and not be filled with rapture in the presence of her who is unrivaled in beauty, and as pure as the angels, the beautiful bride of Lord Oxygen ? ; Would that I could but show you her portrait, but she , shrinks from display. Like the timid maiden of the East, she refuses to unveil. Like the modest wife, she is con- tent that "her husband is known in the gates, when he sitteth among the" elements. She is like the silent i benefactor—"she stretcheth out her hands to the poor, yea, she reacheth forth her hands to the needy." She is like purity itself. The touch of filth does not defile her; { nor can the breath of slander defame her. And though ) her beauty and loveliness may sometimes prove her mis- jj fortune, and those chemical bandits, Sulphur, Chlorine, \ and Phosphorus, may kidnap and carry her off, they find r"' \ 24 CHEMICAL ESSAYS. a constancy they cannot overcome, charms not for them; and, instead of the pleasures they expected to enjoy in her constrained presence, all is acrid and sour; and when her lordly husband comes to her rescue, and consumes these robbers with the breath of his mouth, spotless and unde- filed, his own well-beloved flies to his embrace, and "the heart of her husband doth safely trust in her." But the gentleness, brilliance, stateliness, grandeur, and beauty of this wonderful lady element are all as nothing when compared with her goodness. While others bestow favors for applause, she blesses for the sake of blessing. So gentle, airy, and light, we would expect her to play with the gossamer, or romp with the butterfly, or to soar away up above the clouds, and sport in the blue ether, among the stars and comets. But had she the strength of iron, the gravity of lead, and the caustic energy of chlo- rine combined, she could not undertake or accomplish more than she does. Her power is wonderful, and, like the true lady, she rules only by love; and so gentle is her sway, that her subjects are her willing slaves, and are all unconscious of their servitude. And even her lordly hus- band, with all his energies and passions, is overcome by her affection, and in her embraces he is as gentle as a lamb. Alone, the leaves of the forest wither in the blast of his breath, and nature is defaced by his blighting touch. Soothed by her smiles, he waters the earth, and covers it with its carpet of grass, while the forest is clothed with leaves and flowers, and all nature puts on her holiday garb. Alone, he burns cities to ashes, or crumbles them to dust. Captivated by her gentle sway, he toils like a slave to extinguish the conflagration. Alone, he breaks our ships with his east wind. With her influence and aid, he bears them up, and floats them to the desired havens. Alone, he forges the thunderbolts of war, and hurls them forth on their errands of death. With her, he quenches the ► LADY HYDROGEN. 25 thirst of the wounded and dying, and cools the parched lips and fevered brows of the hospital's inmates. Alone, he devours the widow's bread, and destroys the fruits of the ground to create the demon-drink that fills the world with crime, and changes men to devils. Blest with her genial presence, he furnishes the clear, cool water, which entails only blessings on those who drink it. In many of his grandest and best achievements, he would be utterly powerless, without her presence and her aid. Let us think of this. "In the day that God created" these wonderful ele- ments, positive and negative "created He them, and blessed them and called their name water, in the day when they were created." Life-sustaining, health-giving water! The drink that a God of love has distilled for all his children ! The liquor that strengthens, refreshes, re- vives, invigorates, and purifies. The beverage which has no orphan's tear as its sequel, nor widow's wail as a re- quiem over its fallen victim. A drink that demons do not delight in. The murderer does not imbibe it to pre- pare him for his crime, nor the reveler as a prelude to his midnight debauch. No ghosts of murdered innocents awake from their slumbers to curse the cup that contains it, or the fountain that gushes it forth. Dethroned reason does not curse and babble under its influence; nor does delirium travel in its wake. The lone prisoner does not accuse it of the crime that has brought him to the dun- geon-cell; nor does the felon on the scaffold curse "the moss-covered bucket" for his untimely end. Prisons and almshouses do not overflow with its victims; nor are courts of justice kept busy with its crimes. No! our ~La,dy Hydrogen and her liege lord are, in combined labors of love, far otherwise engaged. Like their divine Creator, they go about doing good. They are his agents in preparing rain and making grass to grow 3 2G CtlEMICAL ESSAYS upon the mountains. By them he visits the earth and waters it, and enriches it with the river of God. They are the messengers by which he sends the mollifying shower and the refreshing dew. Out of them is formed the storm-cloud and the rivers, and the seas and the ocean. Nor are they easily baffled in their benign efforts. They impart power to the majestic steamer, and it stems the river's current, and rides the angry billows. Nor is any work too servile for them, if only it be useful. They turn the mill-wheel and the spindle, and draw the produce of the farmer to the distant market, and return laden with the wares of merchandise. They float the mariner's stately ship and the red man's bark canoe. They wash the poisonous malaria from the atmosphere and the filth from the surface of the earth, to impart health and pro- long life. They never weary in well-doing, but sustain and bless everything that lives, and without their pres- ence life is impossible. And with all their usefulness, they do not forget to be ornamental, nor, while supplying necessities, do they ignore luxuries. They humor all our tastes, and gratify all our senses. They cool the fevered, brow, moisten the parched lips, and quench our burning thirst. And how they charm our sight! By the north wind's aid, they show us the hoar-frost, the ice-crystal, and the snowflake. By the help of the vernal breezes, they paint the flowers, bedeck the forest, and cover the earth with its carpet of green. They hold up the storm-cloud as a background to the rainbow of promise. They furnish " a way for the lightning of thunder," and thus display to us its grandeur. They hang up, as a curtain, the fleecy cloud, and adorn the sunset with its crimson veil. They take up and bear to us the fragrance of the flowers, as sweet as the per- fumes of Araby the blest. And who has not listened with rapture to their music ! LADY HYDROGEN. 27 "What a joy to press the pillow Of a cottage chamber bed, And to listen to the patter Of the soft rain overhead!" Who has heard, elsewhere, such music "As that melody of nature— That subdued, subduing strain, Which is played upon the shingles By the patter of the rain!" And the purling brook, and the warbling rill—whose childhood has not been delighted with their melodies ? And the merry cascade " * * as it gushes, Like a flow of laughter, out—" who has not felt the power, but who can describe the sweetness of its strain ? Thus does our Lady Hydrogen, like a true and faithful wife, co-operate with her lordly husband. His glory is hers, and her proudest thought is of her relationship to him. He is king among the elements, she his early-loved and acknowledged queen. But, though her delight is to assist and co-operate with him, yet when duty calls him from her side, she is neither despondent nor idle. If he kindles a fire for our comfort, she contributes to the fuel. Just think of her going down into the dark caverns of the earth ages ago, and there embracing her dark-eyed brother Carbon, that she might bring him up, at the proper time, to furnish us the heat and light whose comfort and cheer enable us to spend this hour together, and, thus thinking, you can appreciate a little of her self-denial. And, though not able to rule the other elements, like her royal husband, yet she often ac- complishes as much by management as he does by force. 28 CHEMICAL ESSAYS. Is that refractory element, gold, to be subdued ? She coaxes the bandit Chlorine into her service, guides him to the cul- prit, and, during the contest that ensues, returns to the side of her lord. Does chlorine refuse to surrender the captive to the demand of lawful authority? She forms an alliance with Sulphur, another of the banditti, who, over- coming his late comrade, carries off the prisoner, but abandons him to freedom, through fright at the heated anger of Lord^ Oxygen. Is the benighted and bewildered traveler to be warned against fatal bogs and morasses which lie in his pathway ? She plunges into the mire in search of her fiery brother Phosphorus, and, with loving embrace, lures him to the surface, and, in the light of a beacon flash, rejoins her lord. But wrhat shall I say more ? The time would fail me to tell of her marvelous works and her beneficent deeds. She is a wonderful work of a more wonderful Creator. If this is but a passing glance at one of the elements he has made, how extensive the study of them all 1 If this is the lightest and rarest of all, yet possessed of properties wider than the range of our thoughts, and beyond the reach of our comprehension, how vast the field of science which includes the properties of all of them ! Are you, then, discouraged at the prospect ? Do your hearts fail you ? Take courage, my friends I The voyage of the world is a long one—possibly too long for your strength and means—but is that any reason you should not enjoy a pleasure-walk ? There are foreign countries you would like to see. Deprived of visiting them, must you fail to call on your friends in the next village ? The greatest charm of the science we propose to study is its almost infinite extent. It will last us for life ; and I hope it will last us for eternity, and that we will all study it in the same class. But, while it is not possible for you to get through with the study of chemistry in your college LADY HYDROGEN. 29 course which now commences, it is quite practicable for you to acquire such a knowledge of its principles as will make all future study of it a pleasure rather than a toil, and such as will enable you to apply many of these prin- ciples to the wants of the profession to which you aspire. In the months that we are to be together, it will not only be my official duty, but also my special pleasure, to aid you in the study of this science. It is regarded as a dry subject, but you will not find it so, if you endeavor to understand it. In the name of the faculty, I welcome you to our halls. 3* DENTAL CHEMISTRY. From an Introductory Lecture, X855. When material substances are properly studied, they teach lessons of great interest and of the highest import- ance. Man, corporeally considered, is composed of, and surrounded by, matter. It constitutes the whole visible creation, forming a vast field of observation for finite minds. The universe and its Creator may be resolved into two grand divisions, matter and spirit; and two volumes, that of creation and that of revelation, are given us to teach that which we should know concerning them. Each volume teaches much of both divisions. While "the heavens declare the glory of God, and the firmament. showeth his handiwork," we are also taught that "the worlds were framed by the word of God, so that things which are seen were not made of things which do ap- pear." But, as intimated in the outset, we now propose to con- fine our thoughts to the study of matter; and should our minds, as we proceed, be led "through nature up to na- ture's God," it will only evidence that we are properly pursuing and profiting by our lesson. Matter possesses both physical and chemical properties ; and hence we have two corresponding sciences, Natural Philosophy and Chemistry. The physical properties of matter are commonly divided into general and secondary. The general are common to all bodies; the secondary exist only in some. Extension, impenetrability, mobility, indestructibility, extreme divisi- (30) DENTAL CHEMISTRY. 31 bility, gravitation, and porosity are general properties; while softness, hardness, opacity, transparency, color, so- lidity, fluidity, elasticity, density, etc. are secondary. The mechanical philosopher resolves, by virtue of these properties, to make matter act upon matter, for his own accommodation and for the benefit of his race. The hard is made to act upon the soft, the elastic upon the solid, and so on, through the whole list, till the result is the thousands of mechanical appliances which distinguish the enlightened from the savage races. The majestic steamer and the cambric needle, the railway train and the child's rattle, are alike the result of a knowledge of these principles practically applied. The farmer, in view of the divisibility and porosity of matter, pulverizes the earth's surface, that the air and water may be freely admitted to germinate and fructify the implanted seed; and he is rewarded with pastures covered with flocks, and valleys clothed with corn. The astronomer, using the transparency of some and the opacity of other bodies, constructs an instrument with which he surveys the heavens, travels up the milky-way, above the clouds and beyond the sky, wranders from planet to planet, from star to star, and beholds matter, rolled up in worlds, by the plastic hand of Deity, and hurled on its revolving career. A different view is that of the chemist. He, too, studies the properties of matter; but, strictly speaking, he is not concerned with its physical properties. It is his province not to examine what bodies are, but of what they are com- posed. It is his privilege to discover and define the laws by which the Creator controls matter, as body is united with body, forming substances entirely new, as it were, by a sub-creation. Let us, then, for a moment glance at the chemist's field of labor. 32 CHEMICAL ESSAYS. For want of a better mode of expression, we speak of matter being subject to various kinds of attraction; as the attraction of cohesion, which tends to reduce all substances to, and retain them in the solid state; the attraction of gravitation, or that principle which causes bodies sus- pended in the air to fall to the earth; and chemical attrac- tion or affinity. Like cohesion, affinity acts only at insensible distances; that is, substances are brought under the sphere of its influence only by apparent contact. It differs, in this re- spect, entirely from gravitation, which acts at all distances. It differs from cohesion, by its being exerted only between dissimilar particles, while cohesion unites similar particles. For illustration, a block of marble is composed of a vast number of particles, held together by cohesion; and each particle is as really marble as the block itself. But marble is composed of lime and carbonic acid, and these sub- stances are altogether dissimilar, and totally different from marble. They are called the component or. constituent parts of marble; and they are united and held together by affinity. The integral particles of a body are held together by cohesion, the constituent parts are united by affinity. Every chemical phenomenon is produced by the opera- tion of affinity; and hence the chemical properties of bodies are dependent on its action. Its influence extends over all substances, yet it is subject to various modifica- tions. Two substances sometimes manifest no affinity for each other; but a third substance may be added, which has an affinity for both; and a union of all three may be the result. For example, water and oil may be com- mingled, yet they do not unite; but if an alkali be added, a union of the three ensues, and the formation of soap is the result. A substance often manifests unequal affinities for two DENTAL CHEMISTRY. 33 other substances, and it will then quit the one for the sake of the other. A familiar example of this is afforded by alcohol, camphor, and water. The first has an affinity for each of the others; but you all know that when water is added to tincture of camphor, the gum is precipitated, and floats on the surface. The union of two substances, by affinity, is called com- bination ; and the result is a new substance, endowed with properties peculiar to itself. When this change is accompanied by the destruction of a previously existing compound, decomposition is effected. A vast field is here laid open for experiment. It may be ascertained what substances will combine with each other, and in what proportions they unite, and then the properties of the new substances and their affinities must be examined and as- certained. Other substances must next be examined, to ascertain whether they are simple or compound bodies, and if compound, what are their component elements, and by what process they may be decomposed; and finally, after collecting and arranging an extended series of iso- lated facts, general principles may be deduced from them, and the result is the science of chemistry. As the object of the chemist is to examine the relations which affinity establishes between bodies—to ascertain the nature and constitution of the compounds it produces, and to determine the laws by which its action is regulated, it follows that chemistry is the science of affinity. This science not only embraces an extensive field, but admits of a very extended application. It justly ranks as a foundation to other sciences. The farmer, after exhaust- ing his strength and skill, is often pained to find his fields unproductive and his crops light. He applies manure, which imparts vigor to the weeds, but none to the crops j he varies the treatment, and an abundant yield of straw, with but little grain, is the result; he changes again, and 34 CHEMICAL ESSAYS. his crop has not strength to mature; again he tries, and may succeed, after losing successive crops and years of toil, while this science would at once have told him the defects of his soil, and the remedies to apply. The physician may administer a complex prescription, and, to his surprise, witness no results, or results totally different from those expected. An accurate chemical knowledge would allay his surprise, by teaching him that he had commingled incompatible substances. But I need not insist here; for this science is conceded to be an essential part of a medical education. Indeed, it seems to underlie all correct medical attainments. The botanist may classify and ascertain the general properties of plants, and may partially discover their more obvious medicinal virtues; but only the chemist can tell in what element, or compound radical, these virtues exist. He only can elim- inate these hidden principles, the discovery of which has done so much to bless mankind. Only the chemist can travel through both the organic and inorganic kingdoms of nature, selecting the good and rejecting the baneful. 'Tis his province to create, as it were, new bodies, by the union of those already formed; to produce the cooling and healthful salt, from the combination of caustic poi- sons. 'Tis his privilege to discover and apply the anti- dote to the poisonous dose, whether administered by mis- take, or by the hands of villainy. To him society looks for light, when dark suspicion overshadows the death of one of its members; and, by his analysis, the vilest mur- derer, too much of a coward even to stab in the dark, is often detected and brought to justice. The anatomist studies the animal structure, admires the harmonious arrangements of the various organs, grows eloquent over the beautiful adaptation of each to its in- tended use, calls one structure bone, another muscle etc and at last, in endeavoring to penetrate still deeper into DENTAL CHEMISTRY. 35 tho subject, applies to chemistry, to ascertain what sub- stances compose these various tissues; nor does he apply in vain. The physiologist, with laudable industry, endeavors to find out the uses of the various organs; he investigates the laws of life and observes the origin, development, and growth of the animal tissues; and after tracing the whole back to cell formations, his science will carry him no farther. It is then that chemistry is called in to trace these cells, the starting-point of the organic kingdom, back to their original elements in the inorganic. Through his entire course, from the primary cell to the perfect ani- mal of the highest scale, chemistry is the guide and assist- ant of the physiologist. And when his journey is com- pleted, when he has, one by one, examined each secretion, she returns, and lights the pathologist through the mazes and intricacies of diseased life ; ever and anon stopping to enable him to scrutinize each point of interest by the way. She tells him its condition at her late visit with his predecessor, and unfolds its present state, leaving him only, as it were, to compare results and draw con- clusions. I need not mention the influence of chemistry on the arts. You need not be told that it selects the materials for, and prepares the tools of the mechanic; that it pre- pares and mixes the colors for the painter; that it fur- nishes the materials and defines the proportions of the builder's cement; for these are plain to the most super- ficial observer. It is much to all of the arts—it is all to some of them. But the question arises in your minds, "Is it anything to Dental Science ?" Let us then, for a short time, consider its relation to and its influence on the science of our owrn profession. And here you will allow me to premise, in the language 36 CHEMICAL ESSAYS. of another of your professors, that "it has done more to develop and advance dental science than any other agency." Before its dawn, the nature, and of course the treatment, of the principal diseases of the dental organs were veiled in darkness and mystery. Even dental caries was supposed, by men of undoubted ability, to be pro- duced/as that in other bones, by internal inflammation. This science teaches us that it always results from exter- nal chemical action; it detects the causes, demonstrates their action, defines their origin, suggests the remedies, and prepares them to our hand. And in the selection of materials to fill the cavities of decay, and restore the con- tour of the tooth, it manifests no sordid meanness; but directs us to that noble and indestructible metal, gold, dis- carding the whole category of alloys, amalgams, mineral pastes, etc., which none but the unprincipled, and those ignorant of the fundamental truths of this science, ever think of using. This science teaches the dental surgeon the precise con- dition of the various secretions with which he is concerned, their deleterious influence when abnormal, and points out and prepares the appropriate remedial measures. The same science selects the most suitable and only fit materials for artificial bases—prepares them for the me- chanical dentist, and instructs him how to use them. It rejects the dead human, animal, and ivory teeth ; and from the bowels of the earth brings up the flinty rocks, and the metallic oxyds, and from their combinations manufactures the pearly gem, surpassed only by the Creator's gift, the living teeth. But it is needless to specify. A correct knowledge of chemistry will guide you safely in the paths of dental < truth; while those who neglect her teachings, or spurn \ her advice, are left to grope their way through bogs of ; ignorance, prejudice, and error. DENTAL CHEMISTRY. 37 Dental Surgery has taken her stand, and is entitled to rank as an honorable profession; hence, her votaries should be honorable men, and, of course, an honor to their profession. To accomplish this, they must be acquainted with the science of their profession; and this alone should be argument sufficient to induce a careful attention to chemistry. I do not mean that you must understand the whole of chemistry; for that is impossible in our present condition. A young man of respectable talent may com- mence the study in his youth, and pursue it through life, yet fail to overtake it in its onward march. But does this afford a reason for neglecting it ? Far from it. What would you think of the geographer who would abandon his science because he could not visit every city and dis- trict, climb each mountain, and trace each river? That science is advanced by adventurers in different fields, each pushing to the utmost in his favorite direction. But to pursue his subject successfully, each traveler must under- stand the first principles of geography. So it is with chemistry. One applies it to agriculture; another to the mechanic arts and manufactures; another to mineralogy; another to the animal system, and so on. And, as in the former case, each must understand the elementary principles of the science, or totally fail in his effort. While going over the laws of combination, the doctrine of affinity, nomenclature, etc., the student sometimes in- quires, "What has this to do with Dental Chemistry?" The commercial student might with equal propriety make a similar inquiry in regard to the primary rules of arithmetic, by asking, "What has this to do with accounts?" It will be my endeavor, then, to assist you in obtaining, I as rapidly as possible, a correct knowledge of elementary >' chemistry, and in applying it to your professional wants. 4 38 CHEMICAL ESSAYS. If I can aid you in laying a good foundation for future attainments, I shall be satisfied. I trust that I may rely on your attention and co-operation. No one can be more thoroughly aware of the difficulties that lie in our way, or more conscious of incapacity, than myself; yet, relying on your zeal and industry, I expect to succeed. THOUGHTS ON DENTAL CARIES. Dental caries, as ordinarily used, is a misnomer; yet it is more convenient to retain than to abandon its use. A man who has all his life called himself Smith, will find it inconvenient to do otherwise, even when he has dis- covered that his real name is Thompson. The term dental caries was in general use to designate several dis- tinct morbid conditions of the teeth, before we had any accurate knowledge of their nature. And as the principal phenomena of these conditions are well known, and are easily observed, there is little likelihood of mistakes oc- curring in regard to the application of the term. The term caries is usually applied to mortification, or rather to ulceration of bone; and it was applied to decay of the teeth, under the supposition that it results from inflam- matory action. For want of a better term, we still con- tinue it, finding it easier to modify the definition than to change the word. It is now admitted, by all who are familiar with the sub- ject, that, whatever may be the predisposing causes, the immediate cause of dental caries is chemical action. It is well known that constitutional causes have much to do with this disease, both in producing badly organized, de- fective teeth, and in eliminating or preparing the agents which act chemically on them. But no constitution pro- duces teeth so defective that they undergo spontaneous decomposition while retaining a vital connection with the general system. I am aware that a few pathologists still maintain that inflammation of the bony texture of the (39) 40 CHEMICAL ESSAYS. teeth is liable to the same terminations as inflammation of ordinary bony tissue; but it is not profitable to debate this point in the present paper. Suffice it to say that the structure and position of the enamel indicate that the danger is from without, not from within. As soon as it is admitted that decay of the teeth re- sults from chemical action, it is natural to inquire what agent or agents produce this action. Accordingly, we find the profession turned at once in this direction. And when the composition of the teeth is taken into the ac- count, we would infer that the deleterious agents are to be looked for among the acids. And here we have had great confusion of ideas, and are likely still to have it. For example, we are told "that it is proven that nearly all the acids, both mineral and vegetable, act readily upon the teeth." {Harris'' Dictionary, article " Caries of the Teeth.") Upon any part of the teeth ? Or are we to un- derstand that some of them act on the animal portion, some on the earthy, and some, or all, on the enamel ? Just turn to the index of almost any chemical text-book, and ask yourself if it is proved that nearly all of the acids there named act readily upon the teeth. Do carbonic acid, tannic acid, and scores of others that might be named, act readily upon the teeth? This expression, and many others that might be quoted from various writers, show a professional longing for, rather than an attainment of the truth in regard to this matter. Now, for convenience, let us assume that dental caries is produced by the. action of acids. The question still arises, what acids? Are many acids, or only a few, con- cerned in its production? One of the laws of combination teaches us that chemical compounds are definite in their nature. Chemical action is always definite. When an acid combines with an alkali, or base, a definite com- pound, called a salt, is formed. When a different acid THOUGHTS ON DENTAL CARIES. 41 unites with this same base, a different salt is formed. Each salt, each chemical compound of any kind, is dis- tinguished from all others, by characteristics peculiar to itself. It is unlike all other substances, in some respects. Each chemical result differs from all other chemical re- sults. Of course, then, a great variety of chemical re- agents will produce a great variety of chemical reac- tions. Let us now inquire as to the various characteristics of those chemical actions which result in what we recognize as dental caries. Do we here find a great variety of ap- pearances ? Or is it not well known that the phenomena of caries are so few, and so circumscribed, that, by com- mon professional consent, but three or four varieties of it are recognized? We find one variety often called "white decay," and another that is brownish in color, and a third that is very properly designated as " black decay." These differ in other respects as well as in color. In the white variety all the components of the teeth are acted on, and disintegrated, as far as the disease extends. In the second variety, the earthy portion of the tooth seems to be re- moved, while much or all of the animal portion remains, which is conclusive evidence that the chemical agent, whatever it may be, forms soluble compounds with the earthy materials. In the "black decay" there is less dis- integration of the tooth substance than in either of the other varieties; and it progresses less rapidly than either of them. The physical characteristics of this variety, aside from the chemical, would indicate that the chem- ical agent principally concerned in its production forms, mainly, insoluble compounds with the constituents of the tooth. Then, there is a fourth variety, commonly called "chemical abrasion," in which the entire tooth substance is removed, as far as the disease extends. It is evident that the agent producing this, dissolves or forms soluble 4* 42 CHEMICAL ESSAYS. compounds with both the animal and earthy materials of the tooth. Unless we conclude that chemical compounds are not definite in their nature, and that many reagents may pro- duce but a few reactions, we are forced to the conclusion that dental caries, as observed and recognized, results from the action of but few substances on the teeth. It is very probable that each distinct variety is produced by the action of a single agent, and, invariably, by the same agent. I am well aware that more than one variety may be found in the same mouth, at the same time, and in close proximity; and consequently, any given case of caries may partake of the characteristics of more than one variety. It is not uncommon to find "white decay" attacking a tooth in a cavity primarily affected with the brown, or colorless variety. But every practitioner is familiar with unmixed cases, representing all the four classes specified. The physical characteristics of decay depend much on the texture of the teeth affected ; but they are dependent, also, on the nature of the compounds formed by the union of the destroying agent with the constituents of the teeth. The degree of concentration of the chemical agent has also a modifying influence. When much diluted, its action is almost solely in obedience to its strongest affinity. For example, if nitric acid were the agent, when concentrated it would act energetically on the animal as well as on the earthy materials of the teeth ; but when much diluted its action would be almost confined to the latter. The chemical characteristics of decay, however, depend almost exclusively on the character of the agent producing it. The truth of this appears evident, when we reflect that bad teeth and good ones are composed of the same chemical substances. Marble and chalk are alike in chem- ical composition, but not in physical structure; and, THOUGHTS ON DENTAL CARIES. 43 though an acid acts more rapidly on the latter than on the former, yet the result of the action is the same. An acid, too, will act with more energy on a soft, porous tooth, than on one of firmer texture ; yet the chemical re- sults are the same. It is safe to conclude, then, that as there are but few results in the chemical actions attendant on dental caries, there are but few chemical agents im- mediately concerned in their production. It is not to be inferred from the above that but few agents are capable of injuring the teeth by chemical action. Many acids used in food or as medicines are capable of doing injury to the teeth. But no one need suppose that an acid, even though considerably concentrated, brought occasionally in contact with the teeth, is the immediate cause of caries. Every close observer will conclude that caries is the result of an agent acting slowly and steadily in the accomplishment of its work. He will be apt to infer that this agent is either formed by chemical action within the mouth, or is eliminated therein, either as a secretion or an excretion, and that it quietly performs its disastrous deeds as fast as formed or eliminated. The application to the teeth of an acid capable of acting chem- ically on them, facilitates or predisposes to the production of caries; and this it may do, without this acid being the immediate cause of the decay. A tooth may be fractured, or its enamel maybe removed, by mechanical means; and, as the dentine is thus exposed, the tooth is more liable to caries than before the exposure. But no one supposes that the mechanical action which exposes the dentine is the immediate cause of the caries. The dentine would remain sound and healthy, did not some chemical agent attack it. In like manner, in the administration of acids as food or medicine, the teeth may be so corroded as to expose the dentine, and render it as liable to the action of the carious agent as in the former case ; or if the dentine 44 CHEMICAL ESSAYS. is not exposed, the enamel may be roughened, either me- chanically or chemically, so as to afford a lodgment for organic matter, which, by decomposition, may generate one of the acids immediately concerned in the production of caries. On this principle, acid medicines and acid foods may indirectly, but not immediately, cause caries. The same remarks will apply to acids brought in contact with the teeth by eructation or vomiting. If this view is correct, the investigation of the subject of dental caries is brought within a narrower compass than many suppose. The first step is to inquire what acids, in health and disease, are liable to be secreted or excreted, so as to be brought regularly in contact with the teeth. The second is to ascertain what acids are liable to be formed within the mouth, by fermentation or otherwise. And the third is to discover what ones of all these are capable of producing the phenomena of dental caries. There is but little room to doubt that, at least, each of the first three varieties is the result of a specific agent. And if these unstudied remarks should lead others to investi- gate this matter, I will be satisfied. "BUT ONE KIND OF.DENTAL CARIES." Health is a unit, which is about the same as saying health is health. But is disease a unit ? Persons have been found to give an affirmative answer to this question. But such persons agree that while there is but one right way, there may be many wrong ones. A normal tooth is a normal tooth ; but it is capable of undergoing a variety of abnormal changes, differing in nature as well as in de- gree of intensity. And what of it? Nothing, certainly, except that in a prominent place in a well-known journal this remarkable statement is found : " Some authors have labored to divide caries into several different kinds, but there is but one kind—the only differ- ence is in the degree of intensity with which it makes its progress in different individuals and at different periods of life, varying with the habits and constitution of the patient." Notwithstanding this sentence, it is probable that the writer believes that, whatever may be predisposing causes, chemical corrosion is the immediate cause of dental caries. If he does not, space cannot be spared just now to argue with him. It will do for the present to assume as true that which is believed by all scientifically educated dent- ists. And if it is true that chemical corrosion is the cause of dental caries, then there must be as many varieties of corrosion as there are corrodents ; for chemical action is definite, alike in its nature and its results. If but one substance capable of corroding the teeth gets in contact with them, then there can be but one kind of corrosion of (45) 46 CHEMICAL ESSAYS. the teeth; if two, there must be two kinds; and if three, three kinds; and so on for quantities. And the results of chemical corrosion do not depend on "the degree of in- tensity with which it makes its progress," but on the na- ture of the corrodent and the object corroded. If sul- phuric acid corrodes a metal, the metal is oxydized, and a sulphate of the oxyd is formed. This is the inevitable result, let the "degree of intensity" be what it may. That which is true of the corrosion of a metal is true of the corrosion of a tooth. That different agents must produce different results, is simply a chemical truism. If hydrochloric acid corrodes tooth-bone, in the mouth or out of it, it decomposes the carbonate of lime, while it is decomposed itself; and the results are carbonic acid, water, and chloride of calcium, the latter one of the most soluble of salts. At the same time, it forms a soluble compound with, or dissolves, the subphosphate, while it scarcely in- terferes with the composition of the animal matter of the bone. But if sulphuric acid is the corrodent, the carbon- ate is decomposed; but instead of the highly soluble chlo- ride, as above, the almost insoluble sulphate of lime is formed, the subphosphate is not dissolved, and the oxygen and hydrogen are taken from the animal portion, leaving the carbon and nitrogen to dispose of themselves. In short, there is more decomposition, but less disintegration than when hydrochloric acid is the corrodent. These illustrations may suffice for the present. If the doctrine of the sentence quoted above be true, it follows that but one chemical agent is present in the pro- duction of dental caries, and it is probable the writer will have as much difficulty in persuading the profession that this is true, as he would have in convincing us all that there is but one kind of metallic corrosion. He would have this advantage in maintaining the two positions, that " but one kind" of reasoning would be necessary. " BUT ONE KIND OF DENTAL CARIES " 47 Think of him lecturing chemists and druggists after this manner: Some authors have labored to divide the preparations of iron into several kinds, but there is but one kind—the only difference is in the degree of intensity with which the corrosive agent makes its progress in different speci- mens, and at different seasons of the year, varying with the source and texture of the metal. And though this imaginary lecture was delivered* with much earnestness, and great apparent sincerity, and even though every look and action of the speaker showed that he expected to be believed, the druggist's clerk, like an infidel wretch, shook his head, and inwardly resolved that, notwithstanding all this, if a patron asked for per- sulphate of iron, he would not give him the sesquioxyd, even though it is prepared with less inconvenience. DENTAL CHEMISTRY OF THE MOUTH. As the morbid condition which the dental surgeon is most frequently called upon to treat is now universally conceded to be the result of chemical action, and as the most important to be noticed, in replacing the parts lost by its devastations, is the selection of such materials as will neither act chemically on any of the substances within the mouth, nor be acted upon by them, it follows that the chemistry of the mouth, in all its bearings, invites our closest study and the most careful scrutiny. We propose, therefore, to devote some attention to the subject, without any attempt at originality or depth of thought. If we can present the subject in such light that a majority of our readers can comprehend our meaning, and especially if we can render our remarks practically useful, our highest ambition will be gained. And we may as well state here that we do not intend to be either very systematic or techni- cal. We know that many of our readers are not practical chemists, and while they think and reason so clearly for us on other subjects, it will be but small recompense if wo can be useful to them in this. In the discussion of this subject we will avail ourselves of the light of experiments and of the thoughts of others. The teeth are composed of three distinct anatomical elements: the enamel, the cementum or crusta petrosa, and the dentine. These differ from each other both in physical structure and chemical composition. Each is composed of animal matter and earthy salts. The den- tine constitutes the principal bulk of the tooth, and will, therefore, receive our first attention. ' (.48) DENTAL CHEMISTRY OF THE MOUTH. 49 The proportions of organic and inorganic matter vary with the constitution, temperament, and age. As life ad- vances, the calcareous matter is increased ; hence any two analyses are not likely to agree in all particulars. Berzelius found in human dentine : Cartilage and vessels......................................... 28 0 Phosphate of lime, with fluoride of calcium........... 64'3 Carbonate of lime............................................. 5-3 Phosphate of magnesia....................................... 1*0 Soda, with chloride of sodium............................. 1-1 Loss............................................................... 0-3 It is needless to multiply analyses, as this is doubtless sufficiently reliable for practical purposes. But that we may the better understand the subject, it may be profit- able to consider briefly the chemical characteristics of each of the above ingredients. Phosphate of Lime, as its name imports, is composed of phosphoric acid and lime. As the acid and the base unite in several proportions, more thnn one phosphate is formed by their union. As these differ in important re- spects it is proper to know which of them is a constituent of tooth-bone. Phosphoric acid is formed by the union of about 32 parts of phosphorus with 40 of oxygen. Its formula is P05. Lime is composed of 20 parts of the metal calcium and 8 of oxygen, and its formula is CaO. Now, the phosphate found in bony tissues is composed of 224 parts of lime united with 214 of the acid, and its formula is 8CaO -f 3P05. This is not the neutral phos- phate, but is called the subphosphate, or more frequently the "bone phosphate." It may be obtained pure by cal- cining teeth or bones in a crucible to complete whiteness, reducing to powder, and digesting with hydrochloric acid. The bone phosphate is dissolved in the acid, and may be precipitated from it by caustic ammonia. The subphosphate thus obtained is a white, tasteless, 50 CHEMICAL ESSAYS. inodorous powder, insoluble in water, but soluble in acetic, nitric, and hydrochloric acids. It may be precipitated from any of these solutions by ammonia, potash, soda, or their carbonates. It is a very permanent compound, being fused, but not decomposed, by intense heat. Carbonate of Lime is composed of carbonic acid and lime. Carbonic acid is so well known that it need not be described. Its symbol is C02; and hence, the formula of this carbonate is CaO,C02. It exists abundantly in the forms of chalk, marble, etc., and is very readily de- composed by most acids and by heat. Phosphate of Magnesia is composed of phosphoric acid and magnesia. Its quantity in the tooth is not sufficient to modify, practically, any chemical action liable to take place in the mouth. Soda is the well-known alkali, composed of 8 parts of oxygen combined with 23 of the metal sodium. It pos- sesses a strong affinity for acids; but its quantity is so limited that it need scarcely be mentioned in considering the chemical actions by which the tooth is destroyed. Chloride of Sodium is the common table-salt; and, though it sometimes plays an important part in the chem- istry of the mouth, yet but a trace of it is found in den- tine, and hence we will omit its consideration for the present. The cementum or crusta petrosa contains more or- ganic matter, in proportion to its inorganic, than dentine. Its composition, according to Lassaigne, is: Organic matter.......................................... 4218 Phosphate of lime...................................... 5384 Carbonate of lime.................................... 3-98 100-00 As the cementum has less density than dentine, it is more readily acted on by chemical agents; but while the DENTAL CHEMISTRY OF THE MOUTH. 51 mouth retains its normal structure, it is not exposed to either the ordinary or incidental chemical influences within the mouth. Its constituent substances were explained in speaking of dentine. The enamel, according to Berzelius, is composed of: Phosphate of lime, with fluoride of calcium........... 88-5 Carbonate of lime............................................. 8-0 Phosphate of magnesia....................................... 1-5 Membrane, alkali, and water.............................. 2-0 100 00 The extreme hardness of enamel protects it from the action of chemical agents, which would act readily on substances of the same composition having less density. The animal portion of the tooth is possessed, in gen- eral, of the same chemical composition as other organic parts of the body. Albumen, fibrin, and casein consti- tute the principal bulk of animal bodies. It is now gen- erally conceded that these are but modifications of one and the same compound, which is denominated protein, and which is regarded as the starting-point of all tissues. Its composition, according to Mulder and others, is repre- sented by the formula C40H31N5O12. Its equivalent, on the hydrogen scale, is 442-4. The organic tissue of bone, cartilage, etc. is generally included under the term gelatin; but, strictly speaking, this substance does not exist in the animal tissues, but is formed from them by the action of boiling water. The organic portion of the tooth is liable to decomposi- tion from various sources. If its vitality be lost, of course it undergoes spontaneous decomposition, unless prevented by antiseptic measures. The alkalies form with it soluble compounds; and many of the acids, if concentrated, or in their nascent state, are capable of decomposing it, by vir- tue of their affinities for some of its constituents. 52 CHEMICAL ESSAYS. Water, of course, is an ingredient of the vital portion of the tooth, as of all the other organic tissues. In some of the chemical phenomena which occur in the mouth, it plays an important part. Every one knows that it is composed of oxygen and hydrogen—eight parts of the former to one of the latter. Having now briefly noticed the chemical structure of the teeth themselves, the next thing is the chemical char- acteristics of the various agents, either ordinarily or inci- dentally brought in contact with them, which are or may become capable of acting injuriously on them. The first that we will notice is the saliva. Saliva.—The saliva has of late years received much attention from chemists, yet the subject is still somewhat complicated and obscure. It is not our purpose to give a full or lengthy notice of it. "According to Dr. Wright, pure saliva is a limpid fluid, having a faint blue tinge, and a slight degree of viscidity. It is perfectly uniform in con- sistence, and unobscured by frothiness or flocculi." The saliva contains but a very small quantity of solid matter. This is composed of spirit and water-extracts, ptyalin, fat, albumen, sulphocyanogen, and a variety of salts. These salts are usually phosphates, carbonates, lactates, traces of sulphates, and chlorides. Berzelius found in 1000 parts of human saliva : Water...................................................... 992-9 Ptyalin.................................................... 2-9 Mucus.................................................... 1-4 Extract of flesh, with alkaline lactates.......... -9 Chloride of sodium.................................... 1-7 Soda........................................................ -2 Simon found in 1000 parts of his own saliva: Water................ Solid constituents 991-22 8-77 DENTAL CHEMISTRY OF THE MOUTH. 53 These solid constituents were : Fat containing cholesterin............................ -52 Ptyalin, with extractive matter..................... 4-37 Extractive matter and salts........................... 2 45 Albumen, mucus, and cells.......................... 1-40 The saliva varies very considerably in its composition, and no doubt many changes may take place without a forfeiture of its right to the title of normal saliva. Then, its abnormal states are represented by a great variety of modifications. The chemical agents in healthy saliva most important to be noticed, at least as far as the dental chemistry of the mouth is concerned, are water, the chlorides, soda, and sulphocyanogen. Any one who will take the time and pains can, by ob- serving a few plain directions, test the saliva in any given case with sufficient accuracy for practical purposes. And the first thought that strikes the operator is likely to be: "Is the saliva acid, alkaline, or neutral?" This can be usually answered with sufficient accuracy by testing with prepared litmus-paper. And every practitioner should have a supply of " test-papers " in his case ready for use on any occasion that may require them. Nor should he rest satisfied with merely a general examination; but if, for example, he discovers acidity in the mouth, he should go on to ascertain its source, whether it be in the mucus, the saliva, or in decomposing foreign substances. If it- be in the saliva, he should ascertain whether it be in the secretions of all the glands, or confined to but one or more of them. All this he must know, and much more, before he can be at all prepared to treat intelligently any case in which the secretions of the mouth are abnormal. The saliva may be tested for albumen by heat, which, by coagulating the albumen, if present, will render the 5* 54 CHEMICAL ESSAYS. liquid turbid. Sulphocyanogen is indicated by the red- ness produced by the addition of perchloride of iron. Simon says : " With a view to separate the constituents of the saliva, I evaporated a known quantity to dryness, and thus determined the water. I then treated the residue with ether for the purpose of extracting the fat; and with water, in order to take up the ptyalin, extractive matter, and salts. The insoluble residue that had resisted the action of ether and water consisted of albumen and mucus. Another portion of the saliva was decanted from its pre- cipitate, evaporated to a small residue, and the ptyalin, with a trace of extractive matter, precipitated by alcohol." The specific gravity of healthy saliva varies consider- ably. It is generally, if not always, a little above that of water. Pure saliva absorbs oxygen, which contributes to its digestive power. Dr. Wright found that saliva which had been exposed some hours to an atmosphere of oxygen, converted a much greater quantity of starch into gum and sugar, than saliva not so exposed. Morbid Saliva.—The saliva is liable to a variety of ab- normal modifications. It is not our purpose at present to notice all of these conditions, nor any of them at any great length. As already intimated, a free acid, or more than one, may be found in the saliva. The lactic is the most common ; but acetic, hj^drochloric, oxalic, uric, and others are sometimes found. The acid reaction is easily detected by test-paper. Normal saliva, being alkaline, imparts a blue tint to red litmus - paper, while this reddens blue paper. If on evaporation to dryness, the acid reaction is destroyed, it is evident the free acid is not the lactic, which is the most frequently found. Hydrochloric acid may generally be detected by its action on a fresh solu- tion of nitrate of silver; but as the soluble chlorides, if present, would produce similar results, the acid may be DENTAL CHEMISTRY OF THE MOUTH. 55 separated from them and from most of the other con- stituents of the saliva by distillation. Its quantity may then be estimated by the amount of chloride of silver which constitutes the precipitate. Chloride of silver is represented by the formula AgCl, and is composed of 108 parts of silver to 35 of chlorine. The 35 parts of chlorine require one part of hydrogen to form hydrochloric acid; hence when the weight of the chloride is ascertained, the calculation is easy. According to Dr. Wright: " The saliva is impreg- nated with lactic acid, chiefly in gout, rheumatism, ague, diabetes, and gastro-enteritis; with acetic acid in aphtha?, scrofula, scorbutus, small-pox, protracted indigestion, and after the use of acescent wines; with hydrochloric acid in simple gastric derangement from immoderate or im- proper animal food; and with uric acid in gouty affec- tions." He tells us also that acidity of the saliva is likely to occur in fevers, both typhoid and inflammatory, in measles, phthisis, venereal disease, many skin diseases, catarrhs, mumps, and in tedious dentition of weakly children. Mucus.—The internal parts of the animal system which are directly connected with the external, are covered by a soft, velvety, and very vascular tissue, called the mucous membrane. This membrane is a continuation of the skin, and therefore all parts of the system are enveloped in one and the same tegument, its internal and external portions differing very materially in regard to their ex- posed surfaces. The exposed surface of mucous mem- brane is covered by a delicate layer of epithelium. The membrane derives its name from the qualities of the fluid with which it is moistened, which fluid is a regular secre- tion, and serves to protect the delicate membrane from the action of irritants. This fluid is viscid, tenacious, sometimes colorless, but mostly turbid, of a faint yellow 56 CHEMICAL ESSAYS. or grayish-white color. It is secreted in but limited quantities when the membrane is in its normal condition; but in a state of irritation, the secretion is greatly in- creased. It is difficult, if not impossible, to ascertain precisely, either the physical or chemical properties of normal mucus, or even of abnormal. The normal can only be obtained in limited quantities; and the transition from normal to diseased mucus is so gradual and indefinite that it is impossible to define the precise point at which the change takes place. And besides, it is almost impossible to obtain mucus uncontaminated with other substances. It is little wonder then that Simon remarks: "Hence it is not very easy to form a distinct conception of what normal mucus really is." We have said that the mucous membrane is a con- tinuation of the skin; and, like the skin, it is constantly undergoing a desquamation, a separation of cuticular scales taking place in the one, a throwing off of epithe- lium cells in the other. The specific gravity of healthy mucus, when fresh and recently secreted, is greater than that of water; accordingly it sinks in that fluid, unless prevented by the presence of air bubbles or other causes. It was once generally regarded as characteristic of mucus to float in water; and this test was considered sufficient to distinguish it from pus; but dried mucus, or fresh mucus from the intestines or urinary bladder, and even that from the bronchial and nasal cavities, when de- prived of air bubbles, sinks rapidly in that fluid. Fresh, liquid, transparent mucus, from the nasal or bronchial membrane, is found, by examination with the microscope, to consist of a fluid containing minute, rounded, or elongated granular bodies, called mucus-corpuscles, and a more or less abundant supply of epithelium cells. Ac- DENTAL CHEMISTRY OF THE MOUTH. 57 cording to Simon, a finely granulated substance also per- vades the fluid. The mucus of the mouth is obtainable only in such limited quantities, besides being mingled with other sub- stances, that great difficulty is experienced in obtaining a satisfactory knowledge of its chemical properties. Ac- cordingly, nasal, bronchial, and intestinal mucus is gen- erally selected in conducting experiments with this sub- stance. Mucus being secreted by the same membrane, wherever found, is likely to have the same general prop- erties. Simon states that the epithelium cells "are not affected by the addition of water, or of dilute acids; they disap- pear, however, under the influence of caustic alkalies or concentrated acids." These cells are also unaffected by the ordinary earthy and metallic salts. " The mucus-cor- puscles," says Simon, "are very differently acted on. Dilute acetic, oxalic, and tartaric acid speedily deprive the capsules of the mucus-corpuscles of their granular ap- pearance. The corpuscles themselves become round and transparent; the nuclei become apparent, the capsules at length disappear, and the nuclei frequently divide into several granular bodies, so that in place of the mucus- corpuscles previously visible, there are at last only two, three, or more rounded granules to be seen." Simon states that the liquid portion of mucus always exhibits a decidedly alkaline reaction; but this is, at least, doubtful. Indeed, there is scarce a doubt that morbid mucus often has a decided acid reaction. In analysis of mucus the acids are included in the extractive matters. When distilled water is added to a clear fluid mucus a coagulation is perceived which soon is deposited as a fine granular precipitate. The same precipitate, more copious and tenacious, is thrown down by acetic, or almost any 58 ' CHEMICAL ESSAYS. weak acid. This precipitate is not thrown down by the alkalies or their carbonates. The precipitate thus obtained is supposed to be the characteristic chemical constituent of mucus, and is hence called mucin. As mucin is soluble in solutions of the alkalies, and as it is precipitated by removing the alkali by an acid, or even by water, it seems rational to conclude that in normal mucus it is held in solution by an alkali. The fluid portion of mucus also contains chloride of sodium, lactate of soda, and traces of a few other salts. We know but little, positively, of the contents of the mucus-corpuscles. Simon says: "In all probability they contain a fluid in addition to their nuclei. The fat that occurs in mucus is probably contained in the corpuscles; for no fat-vesicles are generally observed in fresh mucus, but after the solution of the corpuscles by the addition of acetic acid, a few fat-vesicles make their appearance." It is probable that fat and albumen, though often found in normal mucus, are not essential constituents of it. By an analysis of nasal mucus Berzelius found in 1000 parts: Water............................................................... 930-7 Mucin............................................................... 53.3 Alcohol-extract and alkaline lactates....................... 3-0 Chlorides of sodium and potassium.......................... 5-6 Water-extract with traces of albumen and phosphates 3-5 Soda, combined with mucus................................... 3.9 1000-0 We have no very thorough and reliable analysis of buccal mucus. It is almost impracticable to obtain mucus from this source in such condition and quantity as will be satisfactory. The analysis of buccal mucus by Jacubo- witsch, as quoted by Piggot, is as follows: DENTAL CHEMISTRY OF THE MOUTH. 59 Water.......................................................... 990-02 Solid matters: Organic matter soluble in alcohol............ 1-67 " " insoluble " ............ 2-18 Fixed salts......................................... 6-13 9-98 1000 00 From the preceding observations we may conclude that mucus contains epithelium cells, mucus-corpuscles, mucin, small quantities of extractive matters, alkaline lactates, chlorides of sodium and potassium, a little phosphate of lime and carbonate of soda, usually a small quantity of fat, and sometimes a trace of albumen. Simon adopts the following method of separating these substances in analysis: "A known weight of mucus must be washed with dis- tilled water and evaporated to dryness on the water-bath. The residue must be finely triturated, and repeatedly ex- tracted with boiling ether, in order to remove the fat; it must then be boiled in spirit of 0 91 as long as any ad- ditional matter is dissolved. The spirituous solution must be evaporated to a small syrupy residue, and alcohol of 0-85 added, in order to precipitate any dissolved mucin, caseous matter, water-extract, and pyin: the alcoholic so- lution, containing the alcohol-extract and lactates, is also to be evaporated. The portion undissolved by boiling spirit of 0-91, consists of mucin with cells, and traces of albumen, if the previous quantitative investigation has shown that this substance is present. " In order to determine the salts,, a portion of the dried residue must be submitted to incineration. It is difficult to obtain a white ash in consequence of the fusion of the salts. The chlorides may be extracted with spirit; the residue must then be treated with acetic acid, in order to convert gO CHEMICAL ESSAYS. the carbonates, which have arisen from the incineration of the alkaline lactates into acetates, which may be extracted with alcohol. Anything that still remains is composed of phosphates and perhaps sulphates, in very minute quantity, together with traces of iron and silica." Irritation of the membrane greatly increases the secre- tion of mucus. This is witnessed in the nasal and bronchial secretions during catarrhal affections, and is often as ob- servable in inflammatory diseases of the mouth. In all these conditions, the mucus is considerably changed. At the onset of the attack, it is thinner than usual, but be- comes thicker as the disease progresses; the mucus-cor- puscles are increased in number and the epithelium cells diminished. Simon says " the reaction continues alkaline; in fact, in most cases it is more strongly so than in the normal state." This is not according to my own observa- tion ; indeed, I have usually found an acid reaction in such cases; but my observations have not been sufficiently extensive to determine what is the rule. There is usually an excess of albumen and an increase of fat. According to our own observation, there is also a very perceptible increase of the soluble chlorides in the early stage of in- flammation of the mucous membrane. Decomposition of these chlorides may take place from adventitious causes; and if so, the nascent chlorine will form hydrochloric acid with the hydrogen of the water contained in the saliva. This may account sometimes for the acid reaction ob- served. Much obscurity rests on this subject, and many diffi- culties lie in the way of its thorough investigation. We hope those who have the time and talent will undertake the task. In our next article we will endeavor to describe the source and action of some of the principal acids which are likely to exert an injurious influence on the teeth. At the close of our article on Mucus, we proposed in DENTAL CHEMISTRY OF THE MOUTH. 61 our next to consider the various articles which, in ordinary life, exert an injurious chemical influence on the teeth. We did not then properly estimate the magnitude of our promise, nor appreciate the numberless difficulties that lay in our way. Having come to our senses in this respect, we now only propose to do something, if we can, toward the fulfillment of our promise. To properly understand any chemical action to which the teeth are subject, it is necessary to bear in mind their texture and composition, and to consider the chemical properties of at least their principal constituents. It must also be remembered that the teeth are endowed with vitality. As dental caries, the most common disease of the human race, is now universally conceded to be the result of chemical action, the importance of this subject is at once manifest. The time is not far distant when in every case of recent caries the enlightened practitioner will be able, by the character of the decay and the habits and constitution of the patient, to detect and identify the agent or agents producing the disease. Any practice short of this knowledge must be at least to some extent guesswork, and is, although the best we can now do, em- pirical practice. The fact that an active alkaline base is the principal in- organic ingredient of the teeth, would indicate clearly that their great danger lies in the presence of acids; and all experience demonstrates the truth of this inference. This danger is also greater from the fact that the principal salt of this base, present in the tooth substance, combines with several acids without undergoing decomposition. It is evident that the acids do not all act alike on the teeth. Indeed, some exert no influence whatever on them, while others act with great energy on each and all of their constituents. It would be an endless task to con- sider all the substances which are capable of exerting an 6 62 CHEMICAL ESSAYS. injurious chemical influence on the teeth; and, perhaps, it would be as unprofitable as endless. All that is now aimed at is an accurate account of the various substances which ordinarily act chemically on the teeth—which pro- duce caries and "chemical abrasion." But without further preface, we will proceed to notice some of the chemical agents alluded to. Nitric Acid.—This acid is composed of five equivalents of oxygen united with one of nitrogen. Its symbol is, therefore, N05. It acts with great energy on all the con- stituents of the tooth. Its great energy of action depends on a variety of circumstances. As an acid, it unites ener- getically with bases, and will, therefore, take the lime and kindred bases from the weaker acids. From its ready decomposition, it affords oxygen, in its nascent condition, for the destruction of oxydizable substances. Its action on the tooth may be thus briefly described: it dissolves the phosphate of lime, decomposes the carbonate, setting the carbonic acid free, and forming nitrate of lime, and destroys the organic portion, producing a highly softened state of the carious matter. In fact, it is a prominent, if not the principal agent in the production of the " white decay." But the question naturally arises, Is an agent so de- structive in its tendencies likely to come in contact with the teeth, and if so, under what circumstances? The question is important, and the answer, perhaps, difficult. It is well known that this acid is frequently adminis- tered as a tonic; and it is a lamentable fact that far too little attention is paid to the prevention of its injurious effects on the teeth in such cases, but this will by no means ac- count for the frequency with which it evidently injures the dental organs. A few thoughts in regard to its for- mation may throw some light on the subject. It is a singular fact that though nitrogen and oxygen DENTAL CHEMISTRY OF THE MOUTH. 63 manifest but little affinity for each other, yet they unite in various proportions, forming at least five well-known distinct compounds. It appears, however, from a variety of circumstances, that their tendency is to unite in the proportions which form nitric acid. The protoxyd is readily decomposed, and yields nitrogen, oxygen, and nitrous acid. The bin oxyd, if brought in contact with the atmosphere, takes from it two equivalents of oxygen, and also becomes nitrous acid, or N04. Hyponitrous acid, N03, on admixture with water, is converted into nitric acid and binoxyd of nitrogen, thus: 3N03 = N05 + 2N02, in which case the latter will be converted into nitrous acid, which, in the presence of water, is converted into nitric acid and binoxyd of nitrogen. It follows from this that, if oxygen and nitrogen unite at all in the mouth, let the proportions be, at the first, what they will, nitric acid must be the ultimate result— as air and moisture, the only agents necessary in the transformation, are here always present. The reader will now think of the mucus, and particles of nitrogenous food lodged about the teeth undergoing decomposition, and yielding nitrogen to the oxygen of the atmosphere, or of the fluids of the mouth, and will con- clude that all is explained. Well, perhaps it is. But let us consider. Nitrogen is emphatically a "conservative" element, and manifests but little tendency to unite with anything, and especially with oxygen. It is probable, therefore, that these two elements unite indirectly. It should be borne in mind that organic nitrogenous bodies contain hydrogen and oxygen, as well as nitrogen. Con- sequently, by their decomposition, these elements are all liberated. The mutual affinities of hydrogen and nitrogen take precedence, and the result is the formation of ammo- nia, NH3. But ammonia, exposed to the action of oxygen, 64 CHEMICAL ESSAYS. is always decomposed; an oxyd of nitrogen being formed, and of course nitric acid is the result. With this view of the case, and from the fact that many persons permit the buccal mucus, as well as particles of nitrogenous food, to remain around, upon, and between the teeth, till decomposition is effected, it is not surprising that the white variety of dental caries is so frequently found. Nitric acid is also sometimes formed in the mouth by the agency of galvanic action. When two metals are placed in the mouth in proximity to each other, and the fluids of the mouth are capable of acting on one of them, galvanic action is established. And if they are so situated that the mucous membrane forms a connecting conductor, by being in contact with both, especially if the metallic surfaces be considerable, a current is established, sufficient to decompose any of the binary compounds contained in these fluids. The liberated nitrogen, hydrogen, and oxygen will result, as above, in the formation of ammonia, and then nitric acid. But galvanic action in the mouth is more likely to develop hydrochloric than nitric acid. This will be noticed again. Sulphuric Acid. — Sulphuric acid is composed of 16 parts of sulphur united with 24 of oxygen. Its symbol is, therefore, S03. In addition to those properties which characterize it as an acid, it is a powerful caustic poison, and promptly destroys the various tissues with which it comes in contact. Its chemical action on ordinary tissues depends principally on its affinity for water, but not altogether; for it has the ability to coagulate and unite with albumen, and to dissolve fibrin. In common with other acids, it has a strong affinity for alkaline bases. With these properties in view, let us examine its action on the teeth. The affinity of this acid for water is so energetic that it DENTAL CHEMISTRY OF THE MOUTH. 65 seems even to force its elements to forsake favorite com- binations, and to unite with each other, that it may be gratified. For example, a cork in a bottle of sulphuric acid becomes dark colored, and is really charred. Now, a cork, like other wood, is mainly composed of carbon, hydrogen, and oxygen—the two latter being in the proper proportions to form water. Their affinity for each other, quickened by that of the acid for the result of their com- bination, causes them to forsake the carbon, unite with each other to form water, and then combine with the acid. The same phenomena occur when it acts on animal tis- sues ; for they are principally composed of the above- named elements, with the addition of nitrogen. Accord- ingly, " black spots are frequently observed in the stomachs of those who have swallowed the acid." Now, that its slow and prolonged action on the gelatinous portion of the tooth would result in its carbonization, is a conclusion justified both by inference and experiment. But carbonized gelatin is " animal charcoal," the color of which is a promi- nent characteristic of "black decay." The phosphate of lime in the tooth, which is not the neutral, but a subphosphate, is not soluble in sulphuric acid; nor is the acid capable of decomposing it, except in the presence of alcohol. It follows, then, that this acid does not break down the texture of the tooth to the ex- tent that some others do, simply because it cannot unite with, or, under ordinary circumstances, decompose the principal earthy salt of which it is composed. And here we have a second characteristic of "black decay." It is now time to inquire whether at all, and if so, by what means, and under what circumstances, this acid is brought in contact with the dental organs. Sulphuric, like nitric acid, is frequently administered as a medicine, and generally with criminal negligence in re- spect to its action on the teeth. But we cannot regard C* 66 CHEMICAL ESSAYS. this as the only or principal source of danger from this acid. If oxygen unites at all with sulphur, the tendency, under ordinary circumstances, is to the formation of sul- phuric acid, as sulphurous acid, in the presence of moist- ure, is rapidly converted into the sulphuric. The whole question, then, is reduced to this, Is sulphur ordinarily present in the mouth, and liable there to become oxy- dized ? Albumen is a constituent of mucus, and is contained in many articles of food. Sulphur, if not a constituent of, is always united with albumen. Its ordinary presence in the mouth is therefore easily explained. Sulphur and oxygen unite directly, under various circumstances, as in the com- bustion of sulphur; but it is probable that the union here is effected by indirect means. Hydrosulphuric acid, or sulphuretted hydrogen, is one of the results of the putre- factive decomposition of albuminous substances. The breaths of our patients often bear ample testimony to its presence in the mouth. Now, the oxygen of the atmos- phere rapidly decomposes this acid by taking its hydrogen to form water. The sulphur is therefore set free, and being in the nascent state, its affinities are increased in energy, and it also unites with oxygen, forming sulphur- ous acid, S02, which in the presence of the water of the saliva is rapidly converted into sulphuric acid, or S03. The quantity of sulphur present in the mouth at any one time is very minute; and a great proportion of this is exhaled by the breath before it has time to undergo de- composition. And sulphuric acid, as already noticed, has a weaker affinity for the constituents of the tooth than some others. Hence "black decay" is not so frequently met with as some other varieties. And as from the na ture of the chemical action the texture of the tooth is not so entirely broken up, the carbonized portion protects the DENTAL CHEMISTRY OF THE MOUTH. 07 parts beneath it. This variety of decay therefore pro- gresses less rapidly than others. Hydrochloric Acid.—This acid is also called chloro- hydric, and muriatic acid. It is composed of 35 parts of chlorine, united with 1 of hydrogen. Its symbol is HC1. Though its elements manifest a strong affinity for each other, yet it is very readily decomposed; and many of its chemical manifestations result from the action of one or both of its liberated elements. It is on this principle the acid attacks metals—being decomposed, the chlorine unites with the metal to form a chloride, and the hydrogen escapes with effervescence. This acid, like those previously considered, is a caustic poison. Its escharotic power depends mainly on its affi- nity for water, which is very active, and on its ability to coagulate albumen. Its chemical action is generally in- ferior to that of the two acids just considered. It unites with bases, forming a class of salts called hydrochlorates; and sometimes it combines with a salt without decompos- ing it, or being itself decomposed. When concentrated, it dissolves animal tissues, but is in this respect far inferior to nitric acid. When much diluted and mixed with dried mucous membrane, it dissolves coagulated albumen, fibrin, etc., performing to all appearance an artificial digestion. A careful observation of these properties will enable us to understand the action of this acid on the tooth. The carbonate of lime and the acid are mutually decom- posed. The results are chloride of calcium, water, and carbonic acid. The decomposition may be represented by the following equation: CaO,C02 + HCl = CaCl + HO + C02. The carbonic acid of course escapes as a gas, and the chloride, being very soluble, is dissolved in the saliva, and thus removed from the tooth. 68 CHEMICAL ESSAYS. The phosphate of lime (bone phosphate), though not decomposed by, is highly soluble in hydrochloric acid. It is dissolved, and is thus removed from the organic portion of the tooth. We have seen that this acid, unless highly concentrated, is not capable of dissolving the animal portion of the tooth. As this concentration is not likely to take place in the mouth, it follows that, when hydrochloric acid is the cause of dental caries, the earthy portion is dissolved and removed, while the animal portion principally remains in the carious cavity. And here we have the prominent characteristics of a third variety of decay. I have not taken into the account any of the earthy salts contained in the tooth, but the phosphate and car- bonate of lime. They are present in such small quantities that they exert but little influence on any of the chemical actions which we have considered. Hydrochloric acid is also administered as a medicine; and the remarks made on the preceding acids apply equally here. This acid is an ingredient of the gastric fluid, and is often present in abnormal quantities in the stomach, from which it is thrown into the mouth by eructation and vomiting. But we cannot thus account satisfactorily for the frequency with which the dental organs are evidently injured by this acid. Though in its normal state the saliva is alkaline, yet in a variety of abnormal conditions it contains one or more free acids; and the hydrochloric is one of those most fre- quently present. It often originates no doubt in the de- composition of the soluble chlorides contained in the saliva and mucus. When the chlorine of these is liberated, it takes hydrogen from the water of the saliva, and this acid is a result of the union. But sometimes hydrochloric acid is directly furnished by the salivary glands, either as a secretion or an excre- DENTAL CHEMISTRY OF THE MOUTH. 69 tion. The system may contain just its normal quantity of chlorine, but if there be a deficiency of sodium or potassium the relative excess of chlorine is converted into hydrochloric acid. In this case the acid is secreted. Or the quantity of potassium and sodium may be normal, with an excess of chlorine. The excess will unite as before with hydro- gen, and the acid will be excreted. At all events, this acid is usually found in the mouth when the mucous mem- brane is inflamed, as well as in patients who indulge in the excessive use of salted meats. Galvanic currents in the mouth always result in the formation of this acid. The chlorides of sodium and potassium, present in normal mucus and saliva, are de- composed, and their chlorine unites with hydrogen derived from the water of the saliva. It is on this principle that we frequently find a decayed surface around a gold filling, which is in close proximity with one of a different metal, or with a silver plate or clasp. In such decays, the animal portion usually remains, while the earthy portion is re- moved, just as would be expected from the prolonged action of dilute hydrochloric acid. In these observations we have endeavored to set forth the results of the ordinary uninterrupted action of these acids on the teeth; and we have seen that they are capa- ble of producing the three varieties of decay usually de- scribed, though we by no means maintain that they are the only agents capable of causing these results. Their actions, and consequently the characteristics of decay pro- duced by them, are doubtless much modified by circum- stances. One of them may be the destructive agent in the commencement of the caries, and, in process of time, another may be developed, and exert its specific influence on the same cavity. Then the phenomena would of course be complex. Again, it should be remembered that a strong affinity for water is a property common to all of them. It 70 CHEMICAL ESSAYS, is possible therefore that carbonization, or blackening, may result from the action of any of them, yet it is by no means probable, at least with nitric acid. But this paper is long enough. We originally intended to include in it the action of several organic acids, but our knowledge of them was too limited; and our experiments with them are not sufficiently matured to enable us to state results with any degree of confidence. Indeed, we find it difficult to conduct some experiments properly, on account of the frequent interruptions incident to the prac- tical duties of the profession. We hope our readers will be patient; but if any one is not, we would be glad to have him turn his impatience to a good account, by anti- cipating us in our experiments, and giving his deductions to the profession. THE ACTION OF TOPICAL REMEDIES ON INFLAMED DENTINE. Read, at the American Dental Convention, August 7th, 1856. Local remedies, generally the main dependence, and often the only resort of the dental surgeon, in the treat- ment of the diseases intrusted to his care, should be care- fully considered and thoroughly understood by him. It is true that constitutional remedies are frequently required in the treatment of dental disease; and it is probable that we are often inclined to neglect the general, and rely on the topical treatment; yet, in inflammation of the den- tine, from the nature of the tissue involved, it is evident that, in a majority of cases, the local is the treatment indicated. The reader will please bear in mind that we now have nothing to say on irritable or exposed pulps, but that our remarks apply only to cases of exalted sensibility of the dentine. For the sake of clearness, let us bear in mind that dentine, like other bony tissue, is composed of animal matter and earthy salts; that it possesses vitality; that its various constituent parts are capable of uniting chem- ically with other substances, and of undergoing chemical decomposition; and that it is sustained in its present state of existence by the combined influences of affinity, cohe- sion, and vital force. Many difficulties lie in the way of reliable experiments, (U) 72 CHEMICAL ESSAYS. in relation to the reactions which take place when chem- ical agents are brought in contact with dentine. It will not do to depend on their action on the tooth out of the mouth ; for then the chemical affinity is not counteracted by vitality. Neither can we rely on the reactions set up by them with gelatin, albumen, or the various earthy salts of which dentine is composed ; for, in that case, affi- nity is counteracted neither by vitality nor by the cohe- sion of the tooth. But, though we cannot learn all that we wish to know from these experiments, still we can learn much that is both interesting and useful. By making due allowance, in each case, for the circum- stances present to modify affinity, and by comparing the results with those we witness in the living teeth, as from time to time these agents are applied, we can arrive at conclusions much more reliable, as a basis for practice, than can be derived from any series of empirical exper- iments, even though it extends to millions of cases and claims the accumulated light of generations. Additional light may also be obtained by noticing the topical action of these remedies on the soft parts, and on the fluids of the system. Local or topical remedies produce mechanical, chemical, and vital effects. It is of the chemical that we propose principally to treat. An agent whose action depends on affinity, even though not capable of producing a chemical change in the tissue to which it is applied, may still be properly ranked as a chemical remedy. The action of a chemical remedy depends on the strength of its affinity for any or all of the constituents of the tissue on which it acts; on the texture of that tis- sue ; on the nature of the resulting compounds, and on the presence or absence of modifying circumstances. Other things being equal, combination takes place with far more energy between liquids, than between a solid TOPICAL TREATMENT OF INFLAMED DENTINE. 73 and a liquid, or two solids. This is because the solid state prevents that closeness of contact necessary to an energetic manifestation of affinity, which acts only at in- sensible distances, and because the cohesion of the solid prevents that mobility of its ultimate particles which is necessary to combination. A soft or porous body is, therefore, attacked by an agent incapable of acting on a more dense one of the same composition. The relative action of a strong acid on chalk and marble will illustrate the point in consideration. The more dense the dentine, then, the greater is its capability of resisting chemical action. The tendency of any substance having a strong affinity for organic matter, when in contact with living tissue, is to overcome the vitality of the part, and unite with one or more of its constituents. Substances capable of producing these changes are called caustics or escharolics. The destruction of vitality in one part produces a change in the vital actions of the surrounding parts, usually result- ing in inflammation, or, at least, in exalted vitality. The whole action of these agents is, therefore, a chemico-vital process. The vital action thus aroused is in proportion to the amount of the disturbance, and to the vitality of the tissue. In the dentine, therefore, the chemical will gen- erally predominate over the vital action; although in some of the soft parts, possessing abundant vitality, the reverse is often the case. The vital force may, in some cases, be able to prevent the escharotic action of these remedies, if they are diluted, or if the energy of their affinity for organic matter be in any way diminished. An immediate chemical change may be thus prevented, and the life of the part preserved; but the vital action is dis- turbed and altered The active force is here still supposed to be affinity, and the effect is termed irritation. A pro- longed application of weak chemical agents, however, will 7 74 CHEMICAL ESSAYS. finally produce slight changes in the composition of the tissues, without causing the death of the altered parts. A caustic may, accordingly, become either an irritant or an astringent, by dilution, or any other means by which the energy of its affinity for organized matter is lessened. Water, albumen, fibrin, gelatin and the calcareous salts are the constituents of dentine, on which the various chemical remedies in use exert their action. And, it may be added, that agents inducing caries expend the force of their affinities on the same constituents. For exampte nitric acid coagulates the albumen, dissolves the phos- phate of lime, and decomposes the carbonate—in short, it acts chemically on every constituent of dentine, and its action ceases only when it is neutralized by the various combinations which take place. The same is true of hy- drochloric acid, but not to the same extent; for a dilute solution of it spends its force almost entirely on the cal- careous portion of the tooth, leaving the gelatinous portion behind. The caustic alkalies act by their affinities for water, albumen, fibrin, and gelatin, which are very powerful; but, having little or no affinity for the earthy portion of the tooth, their action on dentine is less violent than that of most acids. The calcareous matter predominating so greatly, shields the gelatinous portions, to a great extent, from the action of such agents. The action of these agents on solid albumen, etc. is more like ordinary solution than definite chemical combination. The character and texture of the compounds, resulting from the union of escharotics, or astringents, with any or all of the constituents of a living tissue, will, if carefully observed, do much to enable us to select the proper remedy for a particular case. The points important to be noticed are, whether the resulting compound is soluble or insoluble; and if insoluble, whether it be permanent, TOPICAL TREATMENT OF INFLAMED DENTINE. 75 or liable to rapid decomposition. On this point, experi- ments out of the mouth, with medicinal agents, on the various organic constituents of dentine, will give much important information. As an illustration of what is meant, let us compare the action of a caustic alkali with that of creasote, or a kindred substance. It is well known that the alkalies dissolve and hold in solution solid albu- men, fibrin, and gelatin. Now, if one of these be applied to dentine, the animal portion of its substance is dissolved and removed, leaving the surface, with its increased vi- tality, amounting to irritation or inflammation, exposed to the action of the atmosphere, the fluids of the mouth, and any irritating agent that may be brought in contact with it. It is evident, then, that the exalted sensibility of dentine is not likely to be relieved by such agents, un- less applied in quantity sufficient to dissolve the gelatin to such depth that the undissolved calcareous matter be- comes a protecting surface. On the other hand, the application of creasote, or a substance possessed of similar chemical properties, is fol- lowed by a union of the agent with the organic con- stituents of the dentine, resulting in the formation of an insoluble compound, retained in place by its mechanical connection with the calcareous portion of the tooth, form- ing a perfect protection to the parts beneath, which, by excluding all foreign substances, permits the newly aroused vital actions to perform their proper functions, in restoring the parts to health. Another point to be noticed, in this connection, is the fact that the soluble compounds thus formed in dental cavities are liable to be absorbed, and thus produce the specific effect of the remedy on the whole body of the dentine, as well as on the pulp, while the absorption of the insoluble is, in the nature of things, simply impossible. And this leads to the important distinction, already alluded 76 CHEMICAL ESSAYS. to, between the insoluble compounds which are permanent, and those which are readily decomposed. The former, as already stated, cannot be absorbed, while the latter often are. Those formed by the action of tannin, or chloride of zinc, represent the one class—those from arsenious acid, or chloride of mercury, the other. It is important to bear in mind that the agent possess- ing the strongest affinity for the constituents of dentine is not necessarily the most energetic in its action. Tannin manifests a powerful affinity for albumen, fibrin, etc.; but, as the resulting compound is insoluble and permanent, the very energy of the affinity prevents the full force of the remedy, by the almost instantaneous formation of a pro- tective layer, which guards the subjacent parts against the further action of the drug. This remedy is, therefore, practically mild in its operation, its action being neces- sarily confined to a thin superficial layer, whether the quantity used be great or small; yet, to the extent of its combination with the organic constituents of the tissue, vitality is as thoroughly overcome as it could be by the actual cautery. On the other hand, chloride of zinc, though manifesting less active affinity for the organic constituents of dentine, is, at the same time, a far more active remedy. This arises from several causes. It manifests a powerful affinity for water, and in removing this from the dentine, it prepares the way for its own admission, and at the same time is dissolved, and is thus in a better condition for exerting its other affinities, which are in no degree im- paired by its union with the water. The compounds re- sulting from its union with albumen, etc. are more soluble than those formed with tannin, and consequently present a feebler barrier to the action of the remaining portions of the drug. The combination taking place less rapidly, affords time for the agent to penetrate the dentine TOPICAL TREATMENT OF INFLAMED DENTINE. 77 to a greater depth. And besides, the chloride, in contact with organic matter, is gradually decomposed, and thus a limited portion of its chlorine is liberated, and unites with the calcareous elements of the tooth. In the language of Pereira: "The components of the living part, when combined with any of these substances (which form with them insoluble compounds), are less susceptible of decay and decomposition than previously. Hence they are unfitted for the principal property which appertains to their vital condition, viz., that of suffering and effecting transformation." It is on this principle that these remedies exert an antiseptic influence; and it fol- lows that the agent which produces the most permanent insoluble compound with the constituents of the tissue, is the most reliable local antiseptic; while those producing compounds more soluble, and less permanent, often exert a more extended antiseptic influence on large masses of organic matter, simply because they pass into its sub- stance more readily, and to a greater depth. It is well known that the antiseptic influence of tannic acid on the dead skin is perfect, leather being merely tannate of gela- tin, while that of arsenious acid, or chloride of mercury, is imperfect. At the same time, by injecting the vessels of the dead subject with either of the latter substances, putre- faction is for a long time prevented, while an injection of tannin could preserve but little, if any, more than the vascular tissues, on account of its inability to pass out of the principal vessels, owing to the nature of the compound it forms with their organic constituents. Some of the remedies which exert an antiseptic influ- ence act, at the same time, as disinfectants. The chlorides which undergo partial decomposition, when in contact with organic matter, are the most striking examples of this class. The liberated chlorine decomposes the putre- factive agents, and effectually destroys the attendant fetor. 7* 78 CHEMICAL ESSAYS. The carious portions remaining in the cavity, therefore, cease, for the time, to be a source of irritation. This, added to the protecting power of the decomposed layer, which is insoluble, explains the fact that when chloride of zinc or terchloride of gold is used on a diseased surface, whether of the soft or bony tissues, the parts beneath the decomposed surface are found healthier than before the application, and more so than when an escharotic of a different class is applied. By bearing in mind the la'ws of combination, and the doctrine of chemical equivalents, we might be led to con- clude that, when the affinities are equal, the energies of chemical remedies are inversely as their combining pro- portions; but, that the rule may hold good, not only the affinities, but all the modifying circumstances must be equal. It is certainly true, that if two agents manifest equal affinities for the same constituents of dentine, and the resulting compounds are of the same texture, their modus operandi must be the same. In such cases, and only in such, is the activity of the remedies inversely as their equivalents. The equivalent of creasote is 94, that of tannin 212, and the practical activity of the two reme- dies bears some proportion to these numbers; but if we notice the modus operandi of creasote, we will see that its practical energy is much increased by its capability of dis- solving fats and other organic substances, thus removing these obstacles to that intimate contact necessary to chem- ical action. On the other hand, we have seen that but a limited quantity of tannin can be made to act on any sur- face of organized structure. It follows, therefore, that the practical activity of the one is greater, and that of the other less than is indicated by their equivalents. It is hoped that the reader already appreciates the fact that there are important differences, both in the modes and in the results of the action of chemical remedies for TOPICAL TREATMENT OF INFLAMED DENTINE. 79 inflamed dentine. Due discrimination and accurate judg- ment are, therefore, necessary in selecting the remedies for any given case. The state of the general system, the physiological structure, and the pathological condition of the tooth must be understood before it is possible to know the treatment indicated. Then, the remedy most likely to fulfill the indication is to be selected, and, without a knowledge of the modus operandi of each of those from which the choice is to be made, the selection is, at best, but mere guesswork. That we may have a clear understanding of this point, let us briefly notice two or three different conditions of the dentine, which may require treatment. Take, for example, a tooth in which the whole body of dentine is inflamed, or at least has exalted sensibility. Now, it is evident that cutting out the sensitive portion is not the plan for this case; for layer after layer may be removed, till the cen- tral cavity is reached, and the sensibility may be increased during the entire operation. The patient is therefore tor- tured to the limit of endurance, while nothing is gained. Nor is the sensibility immediately relieved by the influ- ence of a remedy whose action is limited to the surface; for when the vitality of a superficial layer is thus de- stroyed, an attempt to remove it demonstrates the fact thaUhe sensibility of the subjacent parts is in no degree diminished, but rather increased. The sensibility in this case, however, may be promptly and totally subdued by an escharotic, which, from its modus operandi, is capable of exerting its action on the deep-seated as well as on the superficial parts; and those who wish to resort to this mode, will find arsenious acid all they could desire. This course, however, seems to us much like that of the woman who strangled her bed-ridden husband, by way of help- ing to ease his misery." The course we prefer, in such a case, is the application 80 * CHEMICAL ESSAYS. of an agent which produces an insoluble and permanent compound with the gelatinous portion of the tooth, thus preserving the parts beneath from the influence of irritat- ing agents, till the case has time to terminate in resolution. This protection should be rendered more complete by the insertion of a soft filling into the cavity; and the term- ination may be much facilitated by constitutional treat- ment. In other cases the exalted sensibility may be confined to the surface of the carious cavity. In such, agents which exert a prompt yet superficial action will accomplish all that is desired. The selection will depend somewhat on the circumstances of the case, and will be better under- stood after the consideration of the individual remedies. In some cases the inflammation is confined to one or more minute points in the cavity. Then the sharp cutting instrument is often sufficient to overcome the difficulty. When it is not, the treatment suggested for the preceding case may be resorted to. In considering the individual remedies for inflamed dentine, we do not propose to notice all that have been or that may be used with advantage, but only a number sufficient to accomplish the various actions indicated, and to meet the ordinary demands of practice. We will not attempt a classification; for in the limited number under consideration nothing could be gained by it. The first that we will notice is Tannin, or Tannic Acid.—Tannic acid is the active principle of vegetable astringents, and is found more abundant in nut-galls than in any other product. It manifests strong affinities. It is soluble in water and alcohol, and slightly so in ether. It unites with albumen, fibrin, and gelatin, forming with them insoluble tan nates. It thus enables us to detect gelatin when dissolved in several thousand times its weight of water. Its medi- TOPICAL TREATMENT OF INFLAMED DENTINE. 81 cinal action is almost necessarily topical; for the prompt- ness of its action on, and the insolubility of its compounds with albuminous substances, prevent its admission into the general circulation. And this is the sole reason that the vegetable astringents are comparatively mild and in- nocuous in their action; for a single grain of tannin, if conveyed directly into the blood, would cause instant death. The action of tannin on dentine has been already ex- plained. Either its watery or alcoholic solution may be used; the latter is the most convenient, in some respects, as the former suffers decomposition by the absorption of oxygen from the atmosphere. Creasote, or Carbolic Acid.—This agent produces its caustic effects by its affinity for albumen and gelatin; and its antiseptic influence arises from the fact that it forms with these substances insoluble compounds. The creasote of former years was obtained from wood- tar; and in some respects it differs from that in present use, which is prepared from coal-tar. The latter is the genuine carbolic acid. Its medicinal effects are the same as those of the wood-tar creasote, while it is not so un- pleasant. It dissolves freely in alcohol and ether, and sparingly in water. Its action may therefore be modified by dilution. The action of creasote on dentine has been already ex- plained ; and, from its modus operandi, it is evident that the popular opinion that it promotes the decay of the teeth is an error. Its other uses do not fall within the range of this paper. Nitrate of Silver.—This salt is a powerful caustic, whether applied to the soft parts or to the bony tissues. Its action is somewhat complex. Dr. Turner imputes its escharotic power to the action of the nitric acid which is liberated by the decomposition of the salt in contact with 82 CHEMICAL ESSAYS. organic matter. This, however, explains but a part of the process; for the salt seems to have a strong affinity for albumen, and unites with it without undergoing decom- position, in the proportion, according to Lassaigne, of 84-5 of albumen to 15-5 of the salt. • This compound is soluble in a solution of nitrate of silver or of chloride of sodium. When the nitrate is applied to the skin, the immediate result is a whitish mark, caused by the union of the salt with the albumen of the cuticle. This soon becomes black, by the decomposition of the salt and the reduction of the oxyd of silver. It is evident, then, that for each atom of silver set free, an equivalent of nitric acid is lib- erated. With these facts before us, we will be able to understand its action on dentine. Let us, then, bear in mind that we have an agent here which acts promptly on the gelatinous portion of the tooth, destroying its vitality to the extent of the combi- nation which takes place; and that by the decomposition of a part of the salt, and the consequent liberation of a part of its acid, it acts also with energy on the calcareous portion. The compound formed by the nitrate with the organic constituents of the tooth is insoluble, except in a few substances, and therefore protects the subjacent parts, as mentioned in speaking of tannin. The precipitation of the reduced oxyd on the surface affords some additional protection. The insolubility of the compound above mentioned pre- vents the absorption of the nitrate by the dentine, and renders its action necessarily superficial. It is not true, then, that its application endangers the pulp, unless the intervening portion of dentine be so thin that it is all re- quired in the chemical union which takes place between it and the remedy; but it is true that its judicious applica- TOPICAL TREATMENT OF INFLAMED DENTINE. 83 tion adds to the safety of the pulp, by relieving the in- flammation of the dentine, which might otherwise be extended to it. When the nitrate is neutralized, by an equivalent of the constituents of the dentine uniting with it, no further chemical action can ensue; but it should be borne in mind that the compound formed by its union with the organic portion of the tooth is soluble in a solution of the nitrate. By applying it in too great a quantity, or too frequently, there may be a greater loss of substance than is desirable or at all necessary; for, as long as free nitrate remains in solution in the cavity, the insoluble compound is not precipitated, and the surface is therefore exposed to its continued action. This constitutes a great practical dif- ference between its action and that of tannin; for we have seen that, however much of the latter may be pres- ent, but a small quantity of it has the opportunity of pro- ducing chemical action. The compound of the nitrate with the organic con- stituents of the tooth is soluble also in chloride of sodium; hence, when the fluids of the mouth abound in this salt, the nitrate does not afford that protection to the subjacent dentine which may be obtained by some other escharotics; and in any mouth, the protection is insufficient, if the sur- face be exposed to contact with food seasoned with the chloride. In view of the above facts, we prefer to use the nitrate in the solid state; and when this is not practicable, we use a concentrated solution in small quantity, in prefer- ence to repeated applications of a dilute one. In consideration of the caustic energy of the nitrate, as compared with that of arsenic—knowing that the latter is often absorbed and destroys the vitality of the tooth—many fear that the pulp is alike endangered from its use. From the remarks already made, we think it is plain that their 84 CHEMICAL ESSAYS. fears are groundless. We will add, however, that all authorities we have been able to consult, agree that it is not absorbed, even when applied to the soft parts, but that its action is necessarily confined to the surface. And further, in acute cases of poisoning, by its internal use, there is seldom, perhaps never, any evidence of its ab- sorption. The subjacent portion of dentine is generally less healthy after the application of the nitrate than after the use of a proper chloride; but, if properly used, the destruction of dentine will be less with the former than with the latter. With a clear understanding of the modus operandi of the nitrate, the practitioner will be at no loss in regard to the cases demanding its use. It acts to a greater depth than tannin or creasote, but not so deep as chloride of zinc, nor does it produce as much pain. Of its action on the soft tissues, we have nothing to say in this paper. Chloride of Zinc.—The chloride of zinc is, perhaps, more frequently applied to dentine than any other caustic. From its modus operandi, it exerts an antiseptic and dis- infectant as well as escharotic influence. Its principal action is on the animal portion of the dentine; yet, as already seen, a part of it is decomposed, and the liberated chlorine may act on the calcareous salts. As its caustic power depends, in part, on its affinity for water, it is milder in solution than in substance; and its action is, consequently, more superficial and less painful. It is soluble in water, alcohol, ether, and chloroform. The ethereal and chloroformal solutions produce far less pain than the chloride in substance. This might be readily expected—its affinity for water being thus overcome, it exerts but a part of its caustic power. Its union with the gelatinous portion of the tooth is also more prompt when thus dissolved; and this may, in part, explain the diminution of pain arising from its application; as the TOPICAL TREATMENT OF INFLAMED DENTINE. 85 ethereal solution of terchloride of gold, which is yet more prompt, causes still less pain. On the same principle, the actual cautery, when very hot, causes less pain and irrita- tion than when of a lower temperature. The ether or chloroform may, however, act directly in lessening the pain by local anaesthesia. In using the chloride, or any other active caustic, it is important to remember the exalted vitality that follows its use. Practitioners are sometimes disappointed in its action, by either delaying the operation too long or begin- ning too soon after its application. The former, we ap- prehend, is the most frequent error. They wait till the exalted vitality commences, but not till it subsides. Now, we regard this as an important point; and it is difficult to lay down definite rules respecting it. It is evident that in the teeth of young persons, and especially in those where the animal matter greatly predominates, the vitality will be more promptly aroused than in those of the oppo- site texture, and, at the same time, the vital change will be greater. Now, if the exalted sensibility be confined to a thin, superficial layer, it may be almost instantly sub- dued by the application of the ethereal or chloroformal solution, and the cavity may be excavated before the vitality of the subjacent portion is excited. But if the operation be delayed till the reaction is established, the tooth is often found in a worse condition for excavating than before the application, and a further postponement becomes necessary. The remarks made on absorption, when speaking of the nitrate of silver, apply with equal force here. There is not the least possible danger from this source—there can be none, even when the chloride is applied to the soft parts. Terchloride of Gold.—Of this substance, we have used only the ethereal solution. It acts with great promptness on dentine, forming an insoluble compound with the ge- 8 86 CHEMICAL ESSAYS. latinous portions; and, by its decomposition, and the con- sequent liberation of chlorine, it acts also on the calcareous salts. On account of its promptness, neither the pain nor the disturbance of the subjacent parts is great. It is, con- sequently, very convenient when the exalted sensibility is superficial. The greatest inconvenience connected with its use is its great liability to decomposition. By expo- sure to air or light, the gold is precipitated in the metallic form. With due care, however, it can be preserved a long time, and it is easily prepared. There is, probably, no danger in its use from absorption ; but a more extended series of experiments and observations are required to warrant a positive statement on this point. Arsenious Acid. — The modus operandi of arsenious acid is involved in great obscurity. In regard to its topi- cal action, Professor Bache says: "Arsenious acid, when it produces the death of a part, does not act, strictly speaking, as an escharotic. It destroys the vitality of the organized structure, and its decomposition is the conse- quence. The true escharotic acts chemically, producing the decomposition of the part to which it is applied: a state incompatible with life." Pereira says: "Though employed as a caustic, yet the nature of its chemical in- fluence on the animal tissues is unknown. Hence, it is termed by some a dynamical caustic." Its escharotic power certainly bears no proportion to its destruction of vitality. That it forms definite compounds with some of the constituents of living tissues, is highly probable; yet, if so, they appear to be readily and rapidly decom- posed, by which means the acid is again free to effect similar results with the subjacent parts of the tissue. Nearly all authorities agree that the topical application of arsenic is liable to be followed by constitutional effects. All dentists admit that the tooth pulp may be destroyed by it, through a wall of dentine of considerable thickness. TOPICAL TREATMENT OF INFLAMED DENTINE. 87 In general, they maintain that, to accomplish this, the agent must, in some way, penetrate the substance of the dentine. Now, as the dentine is endowed with but feeble vitality, it is evident that its life is destroyed by the agent, to the extent that it penetrates it. Consequently, the vitality of a great portion of the dentine may be lost by the use of the remedy, even when the pulp is not reached. The exalted sensibility of dentine is, then, subdued by this agent, more by its vital than by its chemical effects. The leading argument in favor of the use of arsenic for inflamed dentine is its reliability. Well, it is reliable— and no mistake. Whether the augmented sensibility be confined to a spot, a superficial layer, or extend to the whole body of the dentine, it is alike efficient. It subdues the sensibility in these cases, just as effectually as, when sweetened with syrup, or diluted with water, it overcomes the vitality of rats and cockroaches. The exalted vitality, incident to ordinary escharotic action, is not likely to annoy the operator who uses this remedy; for all such reaction is soon subdued by it. As the despot suppresses the earliest uprisings for liberty beneath his iron heel, so this tyrant drug will not tolerate, in the subjacent dentine, even the slightest attempt at rebellion. The most soluble preparations of arsenic are the most energetic; and the quickness with which it acts is in pro- portion to the absorbing powers of the part. It is some- times extensively used as a topical application, without inducing constitutional effects; and, in other cases, the constitutional symptoms are alarming, from the local use of a very minute quantity. The whole weight of authority, we think, demonstrates the fact that the pulp is never safe when it is applied to a carious cavity of a tooth; and, as inflamed dentine may be otherwise relieved, that it should never be applied to a tooth, unless the extirpation of the pulp is indicated. COLD APPLICATIONS TO ACHING TEETH. - 101 Smells and their management.......................................... 171 Soluble quartz............................................................... 192 glass..................................................................... 193 Spirit-lamp explosions..................................................... 141 Styptics........................................................................ 98 Sulphuric acid............................................................... "4 its action on the teeth................................................ 65 theory of its formation............................................. 68 Sulphurous acid......................................................117, 177 Tannin................................................................76,80, 102 "Teeth extracted without pain"....................................... 252 Terchloride of gold.....................................................85, 139 The Bunker family......................................................... I82 260 INDEX. The dental profession and its appropriate work.................... 220 Theoro-practical hints..................................................... 183 The spiritual body......................................................... 237 Topical remedies........................................................... 71 Type metal.................................................................... 191 Ulceration—misuse of the term......................................... 236 Water, eulogy on............................................................ 25 White decay................................................................... 62 Zinc. 190 I '.''*' '.' -.p«P7*'?f:^--! " ••v,:-'''1l.:v.V■•'•';'i-V'V-':".' '■• -;: *.;-..:. i;y :*.-frfii !;:••: >.);■;■ :•■)(:'■.■•'•)r:i:.i;.:-:-:,-'w'i',--:- ^'■''-•^'w