I have also positively ascertained that after the destruction of the brain and spinal marrow in the eel, the heart is susceptible of being impressed through the medium of the ganglionic system. " In an eel, in which the brain had been carefully removed, and the spinal marrow destroyed, the stomach was violently crushed with a hammer. The heart, which previously beat vigorously sixty times in a minute, stopped suddenly and remained motionless for many seconds. It then con tracted ;—after a long interval it contracted again, and slowly and gradually recovered an action of considerable frequency and vigour."* Dr. W. C. Henry has added an argument in favour of the theory of neuromyic action of ano ther kind. It is known that certain narcotics, applied to nerves, destroy the vis nervosa of that part. Dr. henry found that " a solution of opium injected into the cavities of the heart, or introduced into the intestine, immediately arrested the actions of these organs."t It seems difficult to imagine that this effect of the narcotic was not produced through the medium of the nervous fihrillx, the muscular being defended by the internal lining of these organs respectively, in the latter organ, a mucous membrane.
After much consideration given to this subject, we should be disposed to conclude that in the phenomena of muscular action, the stimulus acts upon the nervous fibre, and that the contraction is an effect and the property of the muscular fibre. • If this view be correct, we are necessarily led to consider the vis insita, or muscular power, in connection with the vis nervosa. This latter power is peculiar to certain parts of the nervous system. It is not possessed by the cerebrum or cerebellum, or by the ganglia ; but it exists in the tubercula quadrigemina, the me dulla oblongata, the medulla spinalis, and the muscular nerves. The heart itself has recently been observed by Burdach to contract on sti mulating the cardiac nerves by galvanism.
We owe the discovery of the distinct limita tion of the vis nervosa, or, as he terms it, the " excitabilite," to M. Flourens4 The following were the supposed laws of action of the vis nervosa by Haller, Bichat, and Professor Muller, before I began my own researches on this subject: Haller observes, " Irritato nervo, convulsio in musculo oritur, qui ab eo nerv.oramoshabet." " Irritato nervo, multis musculis communi, totive artui, omnes ii musculi convelluntur, qui ab eo nervo nervos habent, sub sede irritationis ortos. Denique medulla spinali irritata, °nines artus convelluntur, qui infra earn sedem nervos accipiunt ; neque contra artus, qui supra sedem irritationis ponuntur." He concludes,
" conditio illa in nervo, glum motum in muscu lis ciet, desuper advenit, sive a cerebro et me dulla spinali, deorsum, versus extremos nervo rum fines propagatur." And—" ut adpareat meson; motus a trunco nervi in ramos, non a ramis in truncum venire."§ Bichat observes, " l'influence nerveuse ne se propage que de la partie superieure a Fin ferieure, et jamais en sens inverse. Coupez un nerf en deux, sa partie inf6rieure irritee fera contractor les muscles subjacens ; on a beau exciter l'autre, elle ne determine aucune con traction dans les muscles superieurs ; de rnil•me la mobile, divis5e transversalement et en haut et en bas, ne produit un effet sensible que dans le second sens. Jamais l'influence nerveuse tie remonte pour le mouvement, comme elle he fait pour le sentiment." • Lastly, Professor Midler observes, " the motor power acts only in the direction of the primitive nervous fibres going to muscles, or in the direction of the branches of the nerves ; and never backwards ;" and " all nervous fibres act in an isolated manner from the trunk of a nerve to its ultimate branches."-f It is a singular circumstance, that an esta blished fact in experimental research, an esta lished principle of muscular action in the animal ceconomy, should be without application to physiology. Yet such has been the case. For what is the application of the vis nervosa to the explanation of the functions of the animal cecnnomy ? Before any such application could be made, it was necessary that other modes of action of this power should be ascertained. I have, by a series of experiments, determined new laws of action of the vis nervosa, and have thus been enabled to make an extensive application of the principle to the functions of life.
The head of a river tortoise being separated between the third and fourth vertebrx: 1. The dorsal portion of the spinal marrow was laid bare to the extent of one inch below the origin of the brachial nerves ; the spinal marrow was then excited by means of the probe and by galvanism ; both anterior and posterior extremities, with the tail, were moved.
2. A lateral intercostal nerve was then laid bare, and stimulated in the same manner ; the same effects were produced as in the former experiment.
These experiments have been repeated many times, and I performed them in the presence of M. Serres and other gentlemen at Paris, in the month of August, 1839. They establish the following new laws of action of the vis nervosa:— 1. That it does act in the direction from branch to trunk ; 2. That it is in a retrograde direction in the spinal marrow.