CIRCULAR. 
Georgetown, D. C., December, 1848. 
Sir: I have taken the liberty of forwarding to you for examina- 
tion a small pamphlet containing a very imperfect account of certain 
general laws relating to Physiology, which I believe to be new to 
the science. 
I wish to call your serious attention to one of those general laws, 
at this time, that you may be enabled to form some estimate of the 
credibility to be attached to the mere annunciation of the rest. This 
law is: That the action of the living animal fibre consists in exten- 
sion, and not in contraction, as has always been supposed. That 
the subject of investigation may be narrowed down, it is proposed 
to coniine our attention to that form of fibre termed muscular. 
This law was traced out, in the first instance, by reflecting on 
phenomena presented in the human subject, but, as it is still more 
plainly legible in the phenomena to be met with in the lower orders 
of animals, I beg leave to refer to some of the latter. 
It is not designed, in this communication, to enter into any formal 
refutation of the received opinion on this subject, or into an elabo- 
rate argument in support of our position; it is merely intended 
to enumerate some few instances, out of many, in order to facilitate 
your reference to them, with the details of which you are, no doubt, 
familiar. 
If, on a closer examination than you have heretofore given to the 
explanations found in books of some of the functions of those ani- 
mals, you shall discover that such explanations are in the highest 
degree absurd, and that no other explanations can be given with our 
present understanding of the laws of the animal economy, you may 
come to see the necessity of amending those laws, by adopting the 
one which I have proposed. 
We will first enumerate some instances of the action* of the vol- 
untary straight muscles. 
*The condition of a muscle, when in a state of action, has been so little attended 
to, I might say, so entirely misapprehended by Physiologists, that I shall be ex- 
cused for calling attention to it,,./ 
When its cause of action oil the nervous fluid is determined to a muscle, it is 
elongated, and, if the innervation is carried to a certain extent, it becomes stiff and 
rigid ; in extraordinary exertions the muscle becomes as firm and inflexible as a 
rod of steel. M. Brussais evidently alluded to this state of the organ when he 
used the term, "vital erection," although he seems to have formed no definite 
notion of its actual condition, or of the nature of its cause. The increased flow of 
blood is clearly referable to another law of the economy, entirely distinct from 
the one we are now considering. The supply of blood is essential to the due per- 
formance of the function of the nerves, but not at all essential to the action of the 
fibres, which derive their cause of action from the nerves. 
J. & G. S. Gideon, printers. 2 
The eye of the snail, placed at the extremity of its horn, or rather 
a fleshy tube attached to its head, is said to be retracted or drawn 
in by means of the retractor muscle, which arises from what is 
called the foot of the animal, and is inserted at the extremity of this 
horn or tube. 
The protrusion of the eye is said to be effected by the contraction or 
constriction of the circular fibres of the horn immediately behind it. 
Not to dwell on the absurdity of this explanation of the latter 
function-on the impossibility that the constriction of the circular 
fibres of the tube should overcome the contraction of the retractor 
muscle, which is largely developed-on the fact, that if this could 
be done, yet the constriction of those fibres must, by compressing 
the optic nerve, effectually prevent the exercise of the function of 
vision, the fallacy of the explanation may be proved by stating one 
simple fact: When the eye of the snail is protruded no contraction of 
the fibres, or constriction of the walls of the tube, are observable. On 
the contrary, it is dilated or expanded; and, by holding the animal 
up between the light and the eye, any one may see, with the naked 
eye, the muscle, with the optic nerve, extended and lying along on 
the lower side of the tube, but not even in contact with the superior 
portion of its wralls in any part of its extent. 
The truth is, the protrusion, as well as the retraction, of this organ 
is effected by means of what is called the retractor muscle. The ani- 
mal determines its nervous fluid to this muscle, and thus causes its ex- 
tension, or withdraws that fluid to its nervous centre, and causes its 
contraction. 
The next instance to which I would refer may be found in the. 
class of animals termed Bryozoa. 
The operculum in these animals is protruded and retracted at 
will, like the eye of the snail. Dr. Arthur Farre, to whom sci- 
ence is said to be indebted for a most accurate and beautiful deline- 
ttion of its anatomy, was much puzzled to find out by what means 
this animal protruded its operculum. Unfortunately for the cause 
of science, the Doctor discovered in some specimens traces of trans- 
verse fibres about the walls of the stomach, which he supposes, by con- 
tracting, forces out the fluid contents of the stomach, and with them 
the operculum. 1 say unfortunately, because, if he had contented 
himself writh simply giving the anatomy of the operculum and its 
muscles, and left the transverse fibres of the stomach alone, some 
one, in contemplating this structure, might have been led to the 
discovery of the general law which I now propose. These animals 
have nothing more to do than to determine their nervous fluid to or 
from the muscles attached to their opercula in order to protrude or 
retract them, and they may make use of the transverse fibres of their 
stomachs to increase the capacity of those organs for the reception 
of the food which flows into them when the opercula are protruded. 
I might refer to the action of the tongue in all animals as instances 3 
of this general law; and, to show that protrusion may be effected by 
the extension of their peculiar fibres, it is only necessary to place 
the finger on the os hyoides, in our own person, and then elongate 
the tongue; but I would particularly refer to the function of the 
tongue of the chameleon. 
The explanations given of the function of this organ by Mr. John 
Hunter, by Cuvier, and by Mr. Houston, in the transactions of 
the Irish Academy, are too improbable to require any particular notice. 
An attentive consideration of the phenomena presented in the 
function of this organ must furnish to any unprejudiced mind the 
strongest proof of the correctness of our position. 
In further corroboration of this point I refer to the tongue of the 
anteater and of the woodpecker-to the muscles by which the limbs 
and head of the terrapin are protruded, and particularly to the 
muscles attached to the valve of the plastrum or lower shell in the 
land terrapin. 
Locomotion in all animals is mainly effected by the extension of 
the muscles; but to give a rational account of that in leeches, worms, 
and in all creeping animals, the law in question is indispensable. 
As intermediate between the straight muscles and the fibres 
placed around the walls of tubes, I refer to the spiral muscles found 
in the trachea of insects, which, by elongation, increase the calibre 
or diameter of those tubes, and by contraction diminish it. 
For the action of the fibres about the walls of the tubes or hollow 
organs, I refer to the sucking stomach of insects which Treviranus 
saw expanded and contracted at will-to similar organs in the leech, 
&c.-to the respiratory organs in terrapins, frogs, &c.-to the genito- 
urinary organs, especially of females-to the cesophagu^ stomach, 
and intestines-to the arteries, &c., &c. In short, notwithstanding 
that it is formally stated, as an axiom in Physiology, that the ten- 
dency of the action of the tubes or hollow organs is to obliterate 
their calibres or cavities, I confidently lay it down, as an incontrover- 
tible fact, that, whenever the vitality of a tube or hollow organ is ex- 
alted, or, in other words, whenever the cause of action or nervous fluid 
is determined to the fibres about the walls of a tube or hollow organ, 
the calibre or diameter of that tube or organ is increased, and that, 
too, in proportion to the determination of the nervous fluid. 
Should you consider the subject of this communication worthy of 
notice, I should be glad to know the result of your reflection upon it. 
Your obedient servant, 
LOUIS MACKALL, M. D.