Bauhaus-Universität Weimar

MODES OF EXPLAINING THEM. 
549 
the optic nerve and the sympathetic. But Mr. Mayo’s experiments 
on the nerves of the eye, with reference to the motions of the iris, in 
which it was shown that these motions are effected by the action of 
the third nerve, and may be excited by irritation of the optic nerve 
(as by stretching it), proved that the phenomenon must be produced 
through the medium of the brain. After dividing the optic nerve 
within the cranial cavity in a pigeon, he was still able to excite con¬ 
traction of the pupil by exerting traction on the portion of the optic 
nerve connected with the brain. The principle of the reflection of 
the irritation from the sensitive upon the motor nerves through the 
medium of the central organs of the nervous system, was, however, 
first shown to be generali}'' applicable in the explanation of all 
motions consequent on sensations, by the researches of Dr. Marshall 
Hall* and myself, published in 1S33, in which the theory was estab¬ 
lished by new facts to be the true mode of explaining a great 
number of known but ill-understood phenomena.*!“ 
A later work [Memoirs on the Nerv. Syst. Lond. 1837,) by Dr. 
Hall contains the continuation of his researches. The facts observed 
by Dr. Hall and myself are very similar, but we differ much in our 
mode of explaining them. I have brought forward arguments in 
favour of the old opinion of the reflection of impressions from sensi¬ 
tive nerves upon motor nerves through the intervention of the central 
organs. Dr. Marshall Hall, on the contrary, in his last work, intro¬ 
duces an entirely new principle into the explanation, which is thereby 
rendered quite distinct from that which I adopt. Volkmann has added 
several important facts confirmatory of the doctrine of reflex action. 
The following is my view of the subject, as given in the former 
edition of this work, together with a sketch of Dr. Hall’s investiga¬ 
tions, and a comparison of the different views offered to explain the 
phenomena:— 
When impressions, made hy the action of external stimuli on sensitive 
nerves, give rise to motions in other parts, these are never the result of the 
* The paper of Dr. Hall, which is here referred to, appeared in the second part 
of the Philos. Transactions for 1833. I first stated my views in the first edition 
of the first part of this work, which appeared in the spring of that year, in the 
chapter on the Respiratory Movements, and more fully in the second part of the v 
work in the following year, 1834, after Dr. Hall’s paper had appeared. A paper 
by Dr. Hall had, however, been read at the Zoological Society on this subject in 
1832; he has, therefore, the priority. Dr. Hall published an account of my 
views, and a comparison of them with his own, in the Lond. and Edinb. Mag. 
vol. x. No. 58. 
j* Here Professor Mfiller is certainly in error. Earlier physiologists have taken 
an extended view of the sympathetic or reflected motions; they have recognised 
the principle of their dependence on an impression conveyed to the brain and 
spinal cord, have distinguished them from the motions dependent on conscious¬ 
ness and volition, and have even indicated the parts of the central organs of the 
nervous system which are capable of reflecting impressions communicated to them 
by sensitive nerves, so as to excite motions. See especially Dr. Henry Ridley 
(Anatomy of the Brain, cap. xviii. p. 162, et seq.), Dr. Whytt (On the Vital and 
other Involuntary Motions of Animals. Edinb. 1751. Works, p. 153, 162, 506, 
and 511). Cullen (Works, vol. i. p. 109, et seq.), and Prochaska (Annotât. 
Aoademicæ, 1784. Opera Minora, 1800. Lehrsätze aus der Physiologie. Wien. 
1797.)—Translatoro
        

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