Some Resemblances betwixt Plants and Animals 
in respect of their Nutrition, 
with 
Some Remarks on the position of the Natural History 
Sciences in Medical Education. 
ADDR'ESS 
TO THE 
MEDICAL STUDENTS 
AT THE 
OPENING OF THE IVIN TEE SESSION, 
UNIVERSITY OF GLASGOW, 
TUESDAY, OCTOBER 28th, 1879. 
BY 
BAYLEY BALFOUR, Sc.D. (Edin.), M.8., 
REGIUS PROFESSOR OF BOTANY. 
GLASGOW: 
1879. ADDRESS. 
Gentlemen, 
on behalf of my colleagues, some words of welcome at the 
commencement of this session—a session, to some of you, the 
entrance upon a course of study of a loftier and more noble 
character than any on which you have hitherto been engaged ; 
to others, a revival of scenes already familiar, and marking 
another stage of progress towards the goal of your ambition; 
to all, a period in that time of intellectual activity, interven- 
ing betwixt the relaxation of school discipline and your 
outset on life which, whether used or misused, must have 
an important influence on your future. 
It is my duty to address to you to-day, 
The obvious intention of the custom of an address at the 
advent of a new session to furnish an opportunity for offer- 
ing encouragement and counsel and advice to those engaged 
on so important a branch of professional study, has been 
embraced by many of those who have preceded me. But I 
have felt that any words of that nature I might utter, would, 
wanting that quality by which age and experience makes them 
impressive, be inappropriate, and, if they did not weary you, 
might fail to enlist your sympathy. I have therefore preferred 
to seek the materials out of which to spin the thread aud weave 
the web of my discourse in those regions of science with which 
lam most familiar; and, in further explanation, it is right 
to state that I appear before you to-day out of due time. 
The duty I now perform ought in proper course to have 
fallen to the lot of my colleague in the Chair of Anatomy 4 
but, as in the somewhat exceptional circumstances of the 
establishment of my connection with this University, it was 
considered inadvisable that I should deliver at the time an 
inaugural address, the present occasion seemed a fitting oppor- 
tunity for the discharge of that duty. 
Since the time, some twenty years ago, when the identity, 
so far as cognisable by any means at our disposal, of the sar- 
code of the animal body with the protoplasm of the plant 
organism was demonstrated, all biological research has pro- 
ceeded in the direction of showing how similar are the vital 
phenomena exhibited in the two kingdoms of organic nature, 
what a fundamental unity of principle there is amidst the vast 
and complex variety of detail, that the faculties of all living- 
matter, however diverse in degree, are yet substantially alike 
in kind; and, indeed, it would be strange were it otherwise, 
when the physical basis of all life is this one substance— 
protoplasm. 
My purpose to-day is to direct your attention to some 
points of similarity in the function of nutrition as exhibited 
by plants and by animals, and to point out to you how 
essentially alike are the processes of digestion and of re- 
spiration in the members of the two kingdoms. I have 
the more readily selected this as subject-matter of my 
remarks, for whilst the outline of these phenomena in the 
animal is, probably from considerations of self-interest, pretty 
well known, a strange and unfortunate misconception is pre- 
valent, not among the general public merely, but also 
amongst many of those whose avocations are more specially 
scientific, as to the exact nature of these processes in the 
plant body—a misconception witnessed to by misleading 
forms of expression and by statements in works on physiology 
of no mean repute, and of recent date, as to the antagonism 
between plants and animals, especially in the latter respect, 
and to which may also, I believe, in some measure be traced 
many of the pernicious ideas (unfortunately too common) 
regarding the value of a knowledge of plant life to those 
whose energies are eventually to be devoted to the 5 
practice of an art which concerns life in its highest 
manifestation. 
It is expedient that in the first place I briefly indicate 
some of the salient features in the process of nutrition in 
animals with which I desire to institute a comparison; for, 
as the time at my disposal is limited, I cannot hope to give 
more than an outline sketch. 
The proximate principles of the food of animals are, as you 
are aware, of two kinds, inorganic and organic. To the 
former class belong water and the various mineral salts, 
whilst the latter may he divided into the three groups of the 
amyloid carbo-hydrates, as starch and sugar; the fatty carbo- 
hydrates; and the albuminates or nitrogenous principles. 
You all know the important generalisation that animals 
must receive their organic food principles ready formed; they 
are unable to manufacture them for themselves. This not, 
however, absolute, for it has been long known that, in certain 
simple forms among the Infusoria, rests the power of con- 
structing organic compounds (carbo-hydrates) out of inorganic 
elements; and recently Geddes has shown that in many 
land-planarians a like power resides. These exceptions, few 
in number though they be, are yet deserving of attention 
as proving the occasional occurrence in the animal kingdom 
of a power markedly resident, as I shall presently point out 
in detail, in certain plants. 
Now these proximate principles combined in food as taken 
into the animal body are not in a form to be directly applied 
to the repair of the waste tissue and to the maintenance of the 
organic activities of the body. The water and mineral salts 
(after solution) may be at once absorbed, but the organic 
principles must be subjected to the influence of a series of 
conditions by which their chemical constitution is altered, 
their physical character is changed, and they are rendered 
fit to serve their part in the nutrition of the animal—they 
are digested. 
The most important factors in this process of transforma- 
tion are the various animal juices with which the food 6 
comes in contact. The number and character of these vary 
with the position of the animal in the scale of complexity; 
and they act in virtue of certain matters dissolved in their 
substance which are capable of exciting chemical changes in 
the food elements. These contained bodies, the composition 
of which no analytical method has as yet determined, and 
consequently their actual mode of working is unknown, are 
classed as ferments, and the process of digestion which they 
incite is essentially one of fermentation. The ferments known 
in the animal body are numerous, but in correspondence with 
the three classes of organic food principles we may consider 
those that are immediately concerned with their digestion as 
falling into the three classes of (a) the amylolytic, (b) the 
emulsive, and (c) the albuminosic, the ferments of any one 
class being capable of acting upon but one kind of food 
principle, although ferments of more than one class may be 
present in any one animal fluid. 
Of the amylolytic ferments—those which act upon the 
starch and sugar of the food—there is in the saliva, jptyalin, 
which effects the transformation of starch into grape sugar, 
whilst in the intestinal juice a ferment which causes the 
inversion of cane sugar is found. 
In the pancreatic juice a ferment of the second class 
exists, the special province of which is to emulsionise the fatty 
principles of the food. 
Lastly, the albuminous principles are converted into soluble 
peptones by means of the pepsin of the gastric juice. 
The illustrations I have selected of these ferments are 
prominent examples—one from each class as they occur in 
the higher groups of mammals, for there they have been 
most studied and are best known. But investigation is daily 
making it clear that in all animals there are similar ferments, 
differing in amount and intensity of power in accordance with 
specific habits and faculties. It must, however, be borne in 
mind that ferments of other kinds occur in the animal body 
which possibly play a more or less important part in nutrition, 
but of them our knowledge is at present imperfect, and more- 7 
over, it is not necessary for my present purpose to take note 
of them. 
As an outcome of this process of digestion, the food prin- 
ciples are brought into a form suitable for absorption. The 
nutrient portion of the food is then strained off into the blood 
as the internal medium by which transit is accomplished, and 
the recuperative particles are carried to the various parts of the 
body. The nutrient molecules at the seat of final distribution 
transfuse the walls of the delicate capillaries into the surround- 
ing tissues, and at the same time the effete matter which func- 
tional activity entails is transfused as waste product into 
the blood, and removed in its current, to be finally eliminated 
and excreted from the organism along with the residue of 
non-nutrient material taken into the body with the food 
elements. The blood thus has the twofold function of acting 
as a current of supply of pabulum to the tissue, and as a 
system of drainage for effete matter. What kind of food 
particle is requisite for any tissue concerned in any one 
particular form of energy, and how the food particles are 
ultimately homologated with tissue substance, is still hypo- 
thetical. 
Now, in the combustion, which work done by the tissues 
involves, and in the development of heat necessary for life, 
there is always an evolution of carbonic acid. The accumula- 
tion of this gas is prejudicial, nay, fatal, to the economy, and 
its removal is therefore imperative. This, too, is effected by 
the blood, which also brings to the tissues the quantity of 
oxygen requisite for the transference of energy and the con- 
tinuance of activity. The blood thus acts as a carrier of 
carbonic acid from, and a bearer of oxygen to, the tissues; 
the capability of the blood for the latter function depending 
upon the affinity for oxygen possessed by the hemoglobin 
attached to its red corpuscles. 
This interchange of gases constitutes the phenomenon of 
respiration—an oxidation process—required for the perform- 
ance of function and the production of animal heat, and 
therefore for the life and growth of the organism; and the 8 
animal is unable to sustain life for any lengthened period 
in absence of, or with insufficient supply of oxygen. The 
balance between supply and demand for oxygen is kept 
up in the lungs, or in whatever organ may take their place, 
and there it is that the interchange betwixt the gases of 
the blood and those of the medium in which the animal 
lives is accomplished, a process commonly spoken of as respira- 
tion, but which is more properly termed, external respiration, 
as distinguished from those deep-seated changes between the 
blood gases and the tissues, which is the true or internal 
respiration. 
In those simpler animal organisms, where no closed vas- 
cular system exists, the general terms of the problem are 
the same. Digestion is, however, followed by direct absorp- 
tion of nutrient matter over an extended area of the body, 
and the interchange of gases is associated with no particular 
organ, though the presence of oxygen is as necessary, and the 
concurrent evolution of carbonic acid as evident, as in more 
complex forms. 
Such is a rapid sketch of some of the important features 
in the processes of digestion and of respiration in the animal 
organism; and yon will note that digestion is essentially 
a fermentation effected by ferments severally fitted for the 
different principles of the food, and that coincident with this, 
respiration supplies the oxygen necessary for combustion, 
and the evolved carbonic acid is removed. With this as a 
basis of comparison, let me now endeavour to make clear 
these processes in the vegetable kingdom. 
Here it is of primary importance to distinguish two large 
classes of (a) green plants; (h) those that are not green. To 
the non-recognition of this fundamental difference is to be 
traced much of the confusion which has for so long charac- 
terised commonly-accepted notions on this subject. To a 
casual observer the necessity for the distinction may not 
at first sight appear; for are not green plants the most 
complex and numerous of plant organisms ? Is it not from 
them that we derive onr ordinary conception of a plant ? 9 
This, to a certain extent, is true. Those green plants are 
undoubtedly the most highly organised; in point of number, 
however, they are probably far surpassed by those forms 
which are not green, and of which the various kinds of 
so-called fungus are best known. But as with the presence 
of the green colour is associated a power of obtaining 
materials for nutriment, and probably also a means for the 
regulation of the respiratory process denied those forms 
which are not green, and the groups are therefore separated 
by a physiological, as well as by a morphological character, 
an examination of each severally is demanded. 
First, then, with regard to the green plants, their colour is 
due to a substance of complex composition—chlorophyll- 
attached to the protoplasm of the cell, which may or may 
not be differentiated to small rounded portions, the chloro- 
phyll bodies. From the protoplasm the chlorophyll can be 
easily separated in solution. It is formed under the influence 
of light; a normally green plant when grown in darkness, as 
is familiar to all of you in leaves of celery, or in young shoots 
of asparagus, being etiolated or blanched. In some few cases 
(leaves of ferns and seed-lobes of conifers) when temperature 
and other conditions are favourable, chlorophyll appears to 
be formed in darkness. 
These green plants are able, under suitable conditions, to 
take, and do take in all the substances requisite for their 
nutrition as inorganic compounds—water, carbonic acid, 
ammonia and mineral salts being the chief of these. That 
a small amount of nutrient matter is absorbed as ready 
formed organic compounds is no doubt also true, but the 
quantity so supplied is comparatively small. From inorganic 
elements the plant is able to manufacture the proximate 
organic compounds—the amyloid, the fatty and the nitro- 
genous—for its nutrition, and the mode in which these 
inorganic elements are obtained must now be noticed. 
In presence of light, a constant absorption of carbonic 
acid is going on in the green parts, chiefly in the leaves 
the carbonic acid is decomposed, oxygen is given off, and 10 
the carbon entering into combination with other elements, 
a carbo-hydrate is formed within the chlorophyll cells. It is 
in this manner, by this process of so-called assimilation, that 
green plants acquire the amyloid and fatty principles for 
their nutrition. I say so-called assimilation, for this term, 
to which in animal physiology and in general literature 
quite another signification is attached, has been applied by 
German authors to this deoxidation process—an unfor- 
tunate misuse of a word, as thereby it is not a little 
confusing to read that whilst green plants are able to 
assimilate their food elements, plants which are not green do 
not assimilate. The term has, however, been so generally 
used in botanical literature, that it is impossible now to rectify 
the misapplication. Hitherto the chlorophyll has been 
regarded as the agent by which, in presence of light, this 
decomposition is effected, and many chemical theories in ex- 
planation of the process have been advanced, that most 
commonly received referring the power to iron salts in the 
chlorophyll. But Pringsheim’s recent investigations, by his 
new method of microscopical photo-chemistry, have resulted 
in the interesting and important discovery, still, however, 
requiring confirmation, that chlorophyll has no direct influ- 
ence in this assimilation, and the deoxidising power must 
reside within the protoplasm itself, incorporated, it may be, 
in some as yet unrecognised constituent. What the first 
product of this decomposition and recomposition is—whether 
starch, or sugar, or fat has evoked much discussion. 
Certain is it that in dicotyledonous plants the chlorophyll 
bodies are usually rich in starch granules; whilst on the 
other hand, in the leaves of monocotyledonous plants starch 
granules are not of common occurrence, though grape sugar 
can always be detected; and again in most plants small oil 
globules are found in chlorophyll cells. But on this point, 
too, Pringsheim’s researches throw some light, for he has 
demonstrated an oleaginous matter, which he terms Hypo- 
chlorin, within the protoplasm of the chlorophyll bodies, 
easily extracted from them, and this substance, very sensitive 11 
to light, is, he considers, the primary assimilation-product 
from which the carbo-hydrates are subsequently formed. 
The nitrogen of the atmosphere is not directly absorbed 
by the plant for the manufacture of albuminates; it is pro- 
bable, however, that a certain amount of the required nitrogen 
is obtained by epigeal parts in the form of carbonate of 
ammonia. The main source of their nitrogen is the ammonia 
compounds and nitrates in the soil, which, along with water 
and the mineral salts, are absorbed by the delicate root-fibrils. 
These exercise a selective power, excreting an acid substance 
to bring solid matter into a condition in which it can diffuse 
through the cell walls; and substances thus obtained from 
the soil pass up through the tissues as the crude sap. In this 
way the elements for the formation of nitrogenous proximate 
principles—such as gluten and legumin—are derived, the 
construction of these from the inorganic elements proceeding- 
in cells without chlorophyll as well as within chlorophyll 
cells, no part of the cell being specially concerned, and light 
is non-essential. 
In these ways, then, the proximate organic compounds 
required for nutrition, which are of the same character as 
those wanted by the animal, are by green plants manufactured 
from inorganic elements, though, at the same time, they do 
take in a certain amount of ready formed organic matter. 
The terms of the generalisation thus formulated are therefore 
the inverse of that enunciated for the animal kingdom. 
The faculties of non-green plants, on the other hand, are 
more limited, and, we find, a nearer approach to the animal 
world. The funguses are, as I have said, the most numerous 
members of the group; but into the same category come a 
number of parasitic plants such as scalewort, broom-rape, and 
those plants known as saprophytes, which make of decaying 
vegetable matter a nidus—for example, the bird-nest orchid. 
Of these we may say that like animals they take in their 
organic principles ready formed; they obtain no carbon directly 
from the atmosphere; with the chlorophyll they have lost the 
power of assimilation. Carbo-hydrates, as such, are by them 12 
absorbed, their character varying with the nidus, and in this 
connection it may be noticed that starch is never found 
within the tissues of funguses. Nitrogenous compounds are 
also directly taken up, though the power of manufacturing 
these out of inorganic elements is still in many non-green 
plants retained. How different, then, they are from green 
plants, and how inadequately expressive of the facts of the 
case is the oft recurring statement, “ Plants are the manufac- 
turers, animals are the consumers, in the world’s economy.” 
The proximate principles, then, for nutrition,—starch and 
sugar, the fats, the albuminous bodies,—as they are formed 
within the plant body, are not in a condition proper for 
nutrition. They must be digested, and this is accomplished 
by a process termed metastasis, the true digestion of plants. 
It has been for long known that during the germination 
under favourable conditions of heat and moisture of the seeds 
of cereals, there is a gradual breaking down of the stored 
starch granules, concurrently with a development of grape 
sugar in the tissues. This phsenomenon, familiar in the malt- 
ing of barley, was first shown by Payen and Persoz, to have 
as its cause a peculiar nitrogenous substance which they 
separated from the grain, and named diastase, believing it 
to be a pure chemical ferment. By this fermentation the 
food elements of the grain are prepared to be utilised by 
the growing embryo-plant, and it is a digestive process. 
The capability of isolation of the diastase and its power in 
this state of inciting fermentative changes, indicates that this 
digestion is subject to purely chemical laws, and were a con- 
firmation wanted, we find it in the interesting experiments by 
Claude Bernard as to the effects of anaesthetics upon plants. 
For he has demonstrated that in anaesthetised germinating 
seeds, whilst the protoplasm is rendered inactive, and the vital 
phamomena manifested in growth and development cease, 
the purely chemical process of the transformation of starch 
into grape sugar incited by the diastase continues uninter- 
ruptedly. 
One of the most weighty discoveries in modern plant phy- 13 
siology was made by Sachs, when lie observed that the starch 
granules formed by assimilation in daylight within the chloro- 
phyll bodies in leaves disappeared duringthe succeeding period 
of darkness. From what is now known, there is no doubt 
that during daylight also there proceeds a constant solution 
of the starch granules, but the reconstructive process of assi- 
milation overmatches the destructive, and there results an 
accumulation of starch at the close of day within the chloro- 
phyll bodies. That the factors in this change are the same as 
those found in germinating seeds was reasonably to be in- 
ferred, but the proof has only recently been furnished 
by Baranetzky who has demonstrated the presence of a 
starch-transforming ferment in the cells, not only of the 
leaves, but of the stems of many plants; and we may now 
safely conclude that it is present in all cells, whether con- 
taining chlorophyll, or free of it, in which starch is found, 
and by its action the starch is metamorphosed, and takes a 
soluble and diffusible form. 
In such plants as the sugar-cane and the beet-root, the 
products of assimilation take ultimately the form of cane 
sugar. This substance to be of use must be inverted, and 
this is accomplished by the agency of a ferment identical with 
that found in the animal body. Claude Bernard, who first 
propounded the existence of the inversive ferment in beet- 
root has, by his experiments with anaesthetics, furnished a 
most interesting proof of its existence in the yeast plant, 
which is still capable, when anaesthetised, of inverting cane 
sugar; the unorganised inversive ferment, destitute of sensi- 
bility, continuing to perform its work. In the plant body, the 
digestion of amyloid carbo-hydrates (starch and sugar) is thus 
performed in a manner analogous to that in the animal 
kingdom. 
Hitherto no emulsionising ferment has been identified in, 
or isolated from, vegetable tissue. That such exists there is 
abundant indication, for not only are oil globules observed in 
the assimilating cells, but in numerous seeds, such as those of 
poppy, flax, castor-oil, and others, the reserve materials take 14 
mainly the form of fats and oils, and in that condition are in- 
capable of rendering service to the embryo. That the oil in 
such seeds is, indeed, destined as food to the embryo has been 
plainly determined by Gressner, who watched under the mic- 
roscope in the seeds of Cyclamen the gradual disappearance of 
the oil globules for absorption by the embryo, the process 
commencing in the cells of the cotyledons nearest the growing 
parts. Moreover, the emulsionising power of some substance 
in the seed is shown by the fact that oily seeds, when bruised 
in a little water, readily form an emulsion. Further investi- 
gation will, doubtless, result in the isolation of the ferment, 
whose presence is thus evidenced. 
The occurrence of peptic ferments in plants, which effect the 
metastasis of albuminous bodies, has in recent years attracted 
considerable attention. You are all no doubt cognisant of 
the existence of the so-called carnivorous plants, and of 
the facts regarding them which the elaborate investigations 
of Darwin have made known. Taking for example the 
sundew, there is excreted from the glandular hairs of the 
leaf surface a pepsin ferment, which, acting upon the albu- 
minous constituents of the bodies of insects entangled by 
the viscid matter coincidently secreted from the glands, 
gradually digests them, and converts them into peptones, a 
form in which they may be absorbed and applied to the pur- 
poses of plant life. Here, then, is a marvellous analogy with 
the animal. And yet there have not been wanting those who 
refuse to recognise the importance of these changes to the 
plant, who regard the occurrence of a substance with such 
power excreted by the plant, as too anomalous to be 
accredited, and, even when chemical analysis has placed this 
point beyond the pale of discussion, would still, notwith- 
standing the extended observations of Francis Darwin, 
Eeess, and others, deny the possibility of its proving of any 
service to the plant. Is there any one who would deny the 
existence of a ferment in the saliva, an external secretion, 
and its power of transforming starch into sugar, and will any 
one say that the sugar is of no use in the animal economy ? 15 
Assuredly not. Is it, then, any more extraordinary to find a 
pepsin ferment in an external secretion from the plant body ? 
But our knowledge of the presence of pepsin ferments in 
the vegetable does not rest merely on these carnivorous 
plants. Albuminates are abundant in vegetable tissues, and 
in many seeds, especially in Leguminosse, form a great part of 
the reserve material, which must be digested for the embryo. 
Gorup-Besanez has succeeded in extracting from a species of 
vetch the ferment which promotes this end, and which, when 
isolated, acts very powerfully on animal albuminates. Witt- 
mack has also obtained in large quantity from the papaw 
tree a pepsin ferment which digests albuminates, and this 
substance is of some importance, and as it seems to me 
worthy the attention of the medical profession, for, when 
isolated, it acts not so much on the fibrine of the animal 
body, but, as Lauder Brunton informs me, upon the connec- 
tive tissue, thus affording an interesting scientific explanation 
of an Eastern popular belief that this tree has the property of 
rendering fresh meat tender. 
I have said enough to make it plain to you that the albu- 
minous principles of the food of plants are digested precisely 
as they are in animals, but I will bring before you two other 
illustrations, which are of considerable interest, as affecting 
certain collateral questions. 
There is a group of simple organisms now known as 
Myxomycetes, which at one period of their life history pre- 
sent the appearance of masses of free protoplasm. These 
masses constantly move over the surface of their nidus by 
shooting out lobes of protoplasm, and again retracting them, 
only to protrude them in like manner from another spot. In 
this state they exhibit those features so well known as char- 
acterising some of the simplest forms of animals, such as are 
typified in the Amoeba. We might, in fact, consider this 
mass, this plasmodium as it is termed, of the myxomycete, a 
land-bathybius, had not our marine friend belied his early 
promise, and descended to the realms of the inorganic. These 
masses of variously coloured protoplasm, which may be known 16 
to many of you as constituting on tlie surface of the tanpits 
the flowers of tan, possess a remarkable power, as De Bary 
first pointed out, of ingesting solid particles from which nutri- 
ment is extracted, and these, after a longer or shorter sojourn 
within the substance of the protoplasm, are extruded, by the 
gradual flowing away from them of the mass. This remarkable 
power which for so long had been considered an absolute diag- 
nostic mark of animals, led many to regard these organisms as 
belonging to that kingdom. But their plant nature being 
clearly proved, their nearest allies belonging to the group of 
Fungi, the discovery of their life history effectually disposed 
of what had long remained the only distinction between the 
two kingdoms. The question, whether the ingested matter was 
really made use of by the organism, or was merely accidentally 
included by the protoplasm in its passage over it next natur- 
ally suggested itself. This point has been recently set at rest 
by Kiihne, who has proved the existence of a pepsin ferment 
within the plasmodium, a ferment which, on separation, digests 
albuminous bodies more powerfully than many ferments found 
in invertebrated animals. An important link in the biological 
chain has thus been completed. 
The second illustration to which I would refer is an out- 
come of the prolonged investigation by Nageli into the process 
of fermentation, whereby he has shown that in the cells of 
yeast a large amount of a peptonising ferment exists, a fact 
which, in conjunction with investigation in the same direc- 
tion by Claude Bernard and others, goes far to the elucidation 
of that complex phenomena. But upon this interesting sub- 
ject time does not permit me to enter. 
Amylolytic, emulsionising, and albuminosic ferments exist, 
then, in plants as well as in animals. They are essential for 
digestion in both kingdoms. Without them the proximate 
principles of food lie unavailable for the purposes of life. 
After digestion, the nutritive matters are distributed by 
transfusing the walls of the plant cells —for there is no closed 
vascular system—to the growing points, or, it may be, to the 
reservoirs of reserve material for subsequent use, whilst the 17 
non-nutrient particles, after passing through, various chemical 
changes, take the form of various excretions of the plant 
body. 
What then of Respiration in plants ? The combustion 
which accompanies the growth and development of plants, 
and the consequent production of heat, involves an evolution 
of carbonic acid; a supply of oxygen is therefore necessary, 
as in the case of animals, and it is only when the amount 
of this is sufficient that vital phsenomena normally manifest 
themselves. Respiration is a process in plants—oxygen is 
inspired, carbonic acid is expired—so that the main gases in 
the interchange are the same in the two kingdoms of organic 
nature. 
The phsenomena of respiration are exhibited at all times 
and by all plants, both green and those not green. In the 
green plant, however, assimilation conceals during the day the 
respiratory process; but when with darkness assimilation 
ceases, the respiratory process fully discloses itself. To this 
fact may be ascribed the common misconception of the true 
significance of these functions and the unfortunate confound- 
ing of assimilation and respiration—and this, too, though so 
early as the fourth year of this century, Ingenhouss pointed 
out the relation between the processes. Indeed, the history 
of our knowledge of this subject furnishes a record of con- 
flicting theories, based upon imperfect and faulty experiment, 
the outcome of which has been a general acceptation of the 
erroneous view that respiration in plants is of two kinds—a 
respiration in which oxygen is given off, which is termed 
a day-respiration, and a respiration of which the evolved 
product is carbonic acid, termed a night-respiration. 
The masterly summing-up of the true facts of the case by 
Sachs a score of years ago, led on the Continent to the estab- 
lishment of clearer notions upon the matter; but in this 
country the incorrect ideas of our forefathers are, I regret to 
say, still too widely prevalent, and I therefore the more 
earnestly reiterate the statement that respiration in plants 
is a process of combustion, the main factors of which are 18 
the same as in animals—oxygen is inspired, carbonic acid 
is expired; and this process goes on at all times, so long as 
the plant retains vitality. 
Plants, however, differ from animals in their power of 
living for a considerable time, even for days, when deprived 
of free oxygen; but in such an atmosphere they are unable 
to grow or to develope, and after prolonged exposure they die. 
How far for the simplest forms of vegetable life, the Schizo- 
mycetes (bacteria) and Saccharomycetes (yeast) this holds 
good, it is just now difficult to say in presence of the 
conflicting statements of able and accurate observers. For, 
whilst on the one side many researches, and amongst 
them the most recent, those of Nageli, tend to show that 
under favourable conditions of heat, moisture, and a suitable 
nourishing medium, those forms are enabled both to main- 
tain life and to propagate themselves in the absence of oxygen; 
on the other side it is maintained, and this is supported by 
elaborate and careful experiments, that oxygen is requisite 
for their propagation and growth. 
Betwixt green and non-green plants there possibly exists 
a difference, previously unsuspected, in respect of respiration. 
Whilst the studies of Pringsheim, to which I have already 
referred, show that chlorophyll has no direct influence in 
assimilation, they have resulted in the discovery of what he 
regards as the true and only property of the chlorophyll,— 
to act as a screen interposed to protect the protoplasm of 
the cells from the too strong action of light; and as the 
inspiration of oxygen increases with the intensity of the 
light, the chlorophyll will thereby diminish the intensity of 
the respiration. It thus acts as a regulator of the respira- 
tion, and therefore indirectly promotes assimilation. In non- 
green plants there apparently resides no such factor. 
In the respiratory process the direct interchange between 
the gases of the plant and those of its medium—the external 
respiration, as it is termed—in which the oxygen inspired is 
proportionate to the amount of carbonic acid expired, has 
been distinguished from that intra-molecular, or internal 19 
respiration, the process going on in every cell where meta- 
static changes are in progress, which consists in a constant 
evolution of carbonic acid, and is manifested continually, even 
when the plant is in an atmosphere containing no free 
oxygen, though under such conditions with gradually de- 
creasing intensity, until it ceases with the death of the cells. 
The relation betwixt the external and the intra-molecular 
respiration was for long a disputed problem. But these 
terms are merely expressive of two parts of the same process. 
As a result of the metastatic changes, intra-molecular respira- 
tion, marked by the evolution of carbonic acid, takes place, 
and the oxygen inspired by external respiration is requisite 
for the combustion of the products of the metastasis. In other 
words, whatever may be the actual chemical process and the 
intermediate products, there can be no doubt that metastasis 
is the cause of the intra molecular respiration, and that the 
external respiration is thereby induced. Now, as intra- 
molecular respiration goes on in all digesting cells, the oxy- 
gen must pass to them wherever situated. There is no closed 
vascular system nor medium of transit like the blood, and the 
mode of passage from cell to cell has been looked upon as a 
general diffusion of the gases; but a rather curious discovery 
has been recently announced by Jamieson of a substance in 
plant cells which, like the haemoglobin of the blood, has a 
great affinity for oxygen, and acts as an oxygen-carrier to the 
ultimate tissues—a discovery which, if it be confirmed, may 
lead through further investigation to the establishment of 
other points of striking analogy in the two kingdoms. 
These are the features in the digestion and the respiration of 
plants to which I ask your attention, and you will have per- 
ceived that digestion or metastasis in plants is a fermenta- 
tion effected by ferments fitted for the several food principles; 
and concurrent with this, respiration supplies the oxygen 
requisite for combustion, and the evolved carbonic acid is 
removed. 
I have here endeavoured to lay before you a parallel out- 
line sketch of the processes of digestion and respiration in the 20 
animal and vegetable kingdom, and the likeness is too striking 
to be mistaken. Starting from the one substance, protoplasm, 
the physical basis of all life, wherein is no difference we 
can recognise, but which is, nevertheless, endowed with 
a varying potentiality, in one instance exemplified in the 
development of an animal form, in another of a plant form, 
I have tried to show by one line of evidence how the funda- 
mental unity in structure carries with it a unity in function, 
and that there is no duality of power in the two great kingdoms 
of organic nature. 
It seems to me of some importance to bring out pro- 
minently at the present time this connection between the 
Natural History Sciences, and to point out their true relation, 
one to the other, in view of the wide-spread tendency in many 
quarters to underrate their value in medical education. Time 
was when the duties of a practitioner embraced not merely the 
diagnosis of and treatment of disease, but he was called upon 
to dispense the drugs be prescribed, and had to act as his 
own pharmacist. Then, undoubtedly, was it necessary that 
he should possess considerable knowledge of the systematic 
side of Botany, and have a thorough acquaintance with the 
specific characters and the sources of his medicines. But 
the time is past for Botany to be treated as a mere 
handmaid to Materia Medica. Modern Physiology has laid 
a foundation for the rational administration of drugs, and 
it is their therapeutic action which now more specially en- 
grosses the attention of the profession; and in consonance 
with this aspect of medical science, it is the physiological side 
of Botany, and the morphological, in so far as required for a 
proper conception of the functional, of which a knowledge is 
valuable to the medical student. Plants are no longer to be 
regarded by him as merely objects, designated by long names, 
from which materials for making up prescriptions are derived; 
but as a student of life, he must see in them members of the 
living world endowed with faculties which make them power- 
ful factors in the world’s economy. Botany is to be studied 
as a Biological Science. 21 
As you are all aware, there is at the present time an 
agitation for medical reform, heralded by the plausible cry 
of protection for the public. No one will deny that there 
is room for reform in certain directions, but it is open to 
grave question whether the sweeping changes in the character 
of the tests for medical licence and the modifications of 
the course of study which have been urged would produce 
the effect desired. It is hard to conceive of how lowering 
the standard of examination to a minimum would tend to 
the better protection of the public, or how the exclusion 
from the curriculum of study of those sciences, which even 
the reformers designate the fundamental medical sciences, 
would produce practitioners more fitted for the work of their 
profession. 
It is often argued that such a procedure would relieve the 
now too-hard-pressed medical student, give him more time to 
devote himself to practical work, and save him from “wasting ” 
a year of study. But surely if the medical student found the 
course of study which includes these fundamental sciences too 
great a tax for his powers, he would seek entrance to his pro- 
fession through some portal—of which there are several— 
where the demands are not so severe. Is not the present 
status of the Scottish Universities a refutation of this ? Again, 
would the introduction of a student to the practical work of 
his profession without that mental training which natural 
science offers enable him to acquire more rapidly a knowledge 
of his professional work ? Would not his mind be less able 
to grapple with the problems which are suggested to it ? 
Would not the gain of a year be merely nominal ? No 
one, I take it, will advocate the advantage to a student of 
adopting some special line of medical study before he had 
acquired a knowledge of the general principles of disease. It 
might be said that thereby having more time to devote to his 
limited subject, he would acquire greater experience in it. 
But if such a course would not be expedient, wherein lies 
the benefit to the student of pursuing that special study 
which concerns the exhibition of life by man, before he has 22 
learned something of life as seen in its simpler and more 
general developments ? 
The Scottish Universities, at least those of them that 
have raised their voice in opposition to the proposed lines of 
medical reform, so far as it touches the question of examina- 
tions and the course of study, are accused of being more con- 
cerned with their own interest and the preservation of their 
emoluments and of their monopoly, as it is termed, than with 
the interests of medical education. But I fail to recognise 
the grounds of this argument. The present agitation has no 
such basis as that which culminated in legislation at a former 
period—the protection of the public from quackery, and the 
destruction of the privileges enjoyed by certain corporations. 
The effect of the action of Parliament at that time has been 
to establish free trade in medical education. How can 
a monopoly be maintained now by any one body, when all 
come under the same regulations ? This so-called monopoly 
of the Scottish Universities is, I venture to say, but an ex- 
pression of the success which has attended the thorough 
training given by their system, and when accusations of such 
a character are brought forward, one cannot but suspect that 
underneath this cry for protection for the public there lies 
that of protection from the success of the Scottish Universities. 
I myself do not believe that any equitable plan of reform 
would appreciably affect the present position of the Scottish 
medical schools, so long as they continue to offer to the 
student the advantages of sound training and the oppor- 
tunities for practical work which have contributed so largely 
to their success. The Scottish Universities assume a higher 
position than that of merely having care for self-interest; and 
found their opposition to the proposed alterations upon the 
prejudicial effect which they believe they must have on 
the social status of the medical profession in the future of 
the nation. 
The value of the Natural History Sciences and their position 
in medical education is no new subject of contention, and I 
should not at this time have introduced so trite a matter, for I 23 
cannot profess to advance any new arguments, but for the recent 
utterances in a weekly medical journal of one, from whom, as 
a graduate of a sister University, and for a time an assistant 
upon the teaching staff of this University, a want of apprecia- 
tion in this respect was hardly to be expected. Giving rea- 
sons for the opposition by the Liverpool School to the proposal 
to include the power of granting a medical degree in the 
charter of the new Victoria University, he makes “some 
observations to show that the University of London ought 
to supply the desired degree,” and in the course of these 
he passes a condemnation upon the system of study and 
examination enforced by that body. I have no intention of 
expressing here any opinion upon the character of these tests, 
and had the writer contented himself with a criticism of that 
system, his remarks would have passed as the opinion of a 
teacher in a great provincial school. But leaving the 
particular case of the University of London, the writer 
attacks in somewhat strong terms the principle of the intro- 
duction of the primary sciences into the medical curriculum, 
and appealing to his personal experience of, and connection 
with the Scottish Universities, poses as an illustration of the 
small amount of benefit which these sciences afford to a 
practitioner. But he shall speak for himself. He says: 
“ The examiners seem to think that the medical practitioner 
ought to be a peripatetic encyclopaedia of Botany, Organic 
Chemistry, Mathematics, Natural Philosophy, Zoology, and 
Metaphysics—an excellent preparation, no doubt, for enabling 
the future doctor to treat the measles, manage a forceps case, 
or amputate a leg. I remember being pretty well dosed with 
these subjects myself. What Edinburgh man can ever forget 
the terrors of the Botany examination ? All I can now say 
of the matter is, that my teachers did me a great injustice 
in wilfully compelling me to throw away a vast amount of 
valuable time and brain power in painfully burdening my 
memory with a collection of facts, not one of which has ever 
enabled me to do a patient a halfpenny worth of good, so far 
as I can remember. Ah! we are told, but look what a splen- 24 
did mental training this is! Very likely. We used to be 
told that when we were boys, and had to excogitate from our 
wearied pates stumbling Latin Hexameters and cranky Greek 
lambics, while we could not point out Dresden on the map, 
and knew as much about the Drench Eevolution as we did 
about the Justinian Pandects. Mental gymnastics, forsooth ! 
When a man is nineteen or twenty years of age, it is time he 
dropped these, and began to learn something useful.” 
It needs no great attention to recognise how valueless 
is all this intensity of expression, for it is nothing more, 
in support of the doctrine the writer wishes to advance, and 
as an argument against the present position of the Natural 
History Sciences (for it is with them only I am dealing), in 
medical education. Instead of an indictment against these, 
I venture to think the writer has framed one against himself. 
Pew will be, from what he says, convinced of the injustice 
of his examiners. One is rather tempted to ascribe in- 
justice, were there any, to his own act. For the reference 
to memory “painfully burdened” with facts, and to the 
“ terrors ” of examination, lead one to strongly suspect that 
his mind, never having subjected itself to that discipline of 
the scientific method which so greatly increases its power 
and efficiency, was unable, or at least unwilling, to assimilate 
the matters with which it had to deal, and that his “mental 
gymnastics ” were confined to the acquirement of the “ trick ” 
or “ craft of examinations,” as it has been termed, obtained by 
the system of “ cram ”—a system to which the terrors of not 
only the Botany examination in Edinburgh, but of all ex- 
aminations, are due. And in place of demonstrating the 
worthlessness of the Natural History Sciences in medical 
education, he rather furnishes a warning against “ cram.” 
May one not consider that the writer in his letter does 
himself an injustice, by estimating so cheaply the amount of 
good which has accrued to him from his early college career; 
for it is difficult to believe that the mind at that time, so 
plastic and susceptible, should be uninfluenced by contact 
with scientific facts; and surely it is not reasonable to deny 25 
effect to a cause, merely because one cannot register its 
amount ? 
It is indeed to be regretted that the writer was compelled 
“to throw away a vast amount of brain power,” which 
might have served him now, and prevented his falling into 
the error of confounding the literary with the scientific 
method. This was not to be anticipated from one who, as he 
tells us, speaks with the authority of a fourteen years’ expe- 
rience in teaching the ingenuous youth of this country. But 
his comparison of the mental training from classical studies at 
school with the discipline which the Natural History Sciences 
supply is proof of his failing to recognise wherein lies the real 
value of these sciences in education. It is, I think, hardly 
necessary to point out to an audience such as this the differ- 
ent influence as a training which the learning derived from 
books, and the knowledge acquired by a study of things, as 
immediately made known by nature, have on the mind. 
One certainly expects to find in one who assumes the 
function of criticising and of reforming a system of education, 
a thorough knowledge of the part which each subject in the 
system occupies or is capable of occupying, not only of itself, 
but also in relation to the whole. But when, as in the pre- 
sent instance, a critic displays so gross a misconception of the 
true faculty, which the Natural History Sciences perform 
in medical education, it is, I consider, one’s duty to show at 
what rate to estimate his opinions. 
The grounds of the value of the Natural History Sciences 
in medical education are twofold. In the first place, and 
most important, they supply a mental training which can be 
attained by no other means. The mind is brought directly 
into contact with fact. The student does not merely read 
about a thing, but learns to see for himself what it really is; 
and the fact becoming in this manner known to him, his 
intellect is exercised in drawing inferences from the fact, and 
thus becomes practised in the simplest form of induction. If 
then the Natural History Sciences are to be of use in dis- 
ciplining the mind, it is evident that their teaching must be 26 
thoroughly practical. Take up alone the theoretical side, and 
their power in imparting method is reduced. 
In the second place, as holding the position of the funda- 
mental sciences of life, the Natural History Sciences are of 
value to the medical student. The student studies life’s mani- 
festations in their most simple expressions, and thereby obtains 
an insight into the manner of Nature’s working, which affords 
him a valuable clue to the explanation of many of those com- 
plicated phenomena exhibited in its highest development— 
Man. 
And there is yet another point of view from which the 
Natural History Sciences may be regarded as beneficial in 
education. The beauty of the objects with which they deal is 
well calculated to give us pleasure and delight, which we 
cannot afford to neglect, and should endeavour to cultivate. 
Do not mistake me to say that a knowledge of these sciences 
will of itself augment our appreciation of this beauty. But 
it is of value in furnishing us with a catalogue of the pictures 
in Nature’s gallery, in leading us to search for the beautiful 
in nature, and thereby opening up to us an unlimited field of 
enjoyment and recreation. 
In commencing my remarks I disavowed the intention 
of offering to you counsel or advice, but, ere I close, 
allow me, addressing myself to those who are now entering 
upon their medical studies, to impress upon them the 
importance of a close attention at the outset of their 
career to the Natural History Sciences, which, neglected 
now, can never in future life be properly learned. Some 
there are who press the student at once into hospital 
work, holding that he cannot too early familiarise himself 
with the aspects of disease; and the neglect of the funda- 
mental sciences which such a procedure involves, is, they 
think, amply compensated by the experience acquired. But, 
gentlemen, honest work, upon the foundations of science, 
alone will furnish a basis upon which to build the superstruc- 
ture of the knowledge requisite for the proper practice of 
your profession. Those who hurry into hospital work may 27 
for a time appear to succeed, they may seem to make rapid 
progress, and to have outstripped all who have devoted the 
early portion of their course to scientific work; but be not 
deceived, the advantage is not real, the success is but transient, 
for wanting the broad basis of a general knowledge of life, 
they are unable in the future to appreciate the wide issues 
which the healing art involves; they are apt to practise their 
profession as a mere routine of empiricism; they fail to grasp 
the idea that it is a science as well as an art. 
I have done; and, in conclusion, I congratulate you on the 
commencement of another session. A season of hard mental 
work lies before you. Set to it diligently, earnestly; at the 
same time do not forget that besides the mind, the body 
must be exercised, and do not allow a desire for success in 
your studies to interfere with a due and proper amount of 
recreation. Eemember that to work too much is as hurtful 
as to work too little, that the best work is accomplished when 
the sound mind is associated with a sound body. And in all 
things, in every field in which your energy may be exerted, 
strive to fulfil the precept, “ Whatsoever thy hand findeth to 
do, do it with thy might.”