ON MUSCULAR IRRITABILITY. 161 



The general deduction -warranted by the experiments seems to he, that 

 any mode of death which tends to inteifere with the processes generating 

 muscular force, either by acting directly on the muscular tissue or indirectly 

 by exciting the nervous tissue to the consumption of muscular force, is op- 

 posed to the production of this exalted state ; on the other hand, modes of 

 death which quietly destroy the nervous system by sedation or by with- 

 hoMing its nutrition (blood), and at the same time do not interfere materially 

 with the muscular system, seem favourable to its production. 



The extensive character of the contraction which takes place during this 

 exalted state of muscular tissue appears to result from a propagative action : 

 e. g., in the most sensitive state it is simply necessary to include the smallest 

 portion of a muscle within a pair of forceps, or to touch a single spot with the 

 point of a fine needle, to excite contraction in a considerable portion of the 

 muscular mass. As in the case of the heart, a few fasciculi immediately 

 subjected to stimulation contract, and in the act excite contraction in con- 

 tiguous fasciculi ; and in this way the effect rapidly spreads throughout the 

 muscle, and, by calling into i^lay a large number of elements, induces a marked 

 and continuous contraction allied to that produced by the medium of the 

 nerves. 



The nervous stimulus seems to differ from other modes of stimulation in 

 the effect produced, mainly in the fact that it can call at once into effective 

 action considerable masses of muscular structure by virtue of the minute 

 distribution of its filaments among the muscular elements. In the ease be- 

 fore us a similar effect seems to be brought about by a preternatural degree 

 of exeitabihty on the part of the muscular tissue itself. 



In dealing with my second proposition, it is not my intention to recapitu- 

 late the many arguments which have been adduced to" show the independence 

 of muscular iriitability of nerve-force. I wish simply to demonstrate that 

 in all cases where nerve-influence may be considered in active operation 

 there is a diminution of muscular irritability, and that, conversely, when 

 that influence is cut off from muscle, there is a tendency in the muscular 

 force to accumulate. In all animals there is a marked distinction in the states 

 of the nervous and muscular systems during mental activity, and the condition 



his theory of reflex or excito-motory action. The arguments of Dr. Hall may be briefly 

 summed up thus:— If cold-blooded animals or the young of warm-bloods be decapitated, 

 or their brains removed, irritants applied to their bodies will still induce movements. That 

 the animals have lost the power of volition is maintained on the ground thai they perform 

 no spontaneous movevients ; and inasmuch as volition is the secojid link in the cliain of which 

 sensation is the first and motion the last, the creatures cannot possess sensibility ; there- 

 fore the movements which follow irritation, however purposive or adapted to ends they 

 may seem, are not the result of either sensation or volition, inasmuch as these are proper- 

 ties of the brain alone ; therefore they result from a purely mechanical arrangement, the 

 principle of the operation of which is that any excitation applied to the extremities of 

 sensory nerves is conveyed to the nervous centre and there reflected on to a motor nerve, 

 which in its turn stimulates muscle into action, no sensation whatever being perceived. In 

 respect to these opinions of Dr. Hall, I would remark that, whether or no the absence of 

 spontaneous movement proves the absence of volition, it is quite certain that the converse 

 is true, viz. that the presence of spontaneous movement proves the existence of volition ; 

 and, as seen in the above experiment, the decapitated trunk gives all the evidence we can 

 have or ever do have of the possession of both volition and sensation : the whole theory of 

 Marshall Hall is completely disproved and subverted, and the brain can no longer be re- 

 garded as the exclusive seat of these powers. In order to secure success in this expe- 

 riment, certain precautions are necessary. 1. No anesthetic should be used, as it materially 

 decreases the chance of recovei-y. 2. The hemorrhage must be trifling. 3. Tiie nervous 

 tissue must be cut, not crushed. To achieve these conditions, the angles of the mouth 

 .should be slit sufficiently far back to allow of the removal of tlie head by means of a sharp 

 chisel ; the lower jaw, tongu?, and principal vessels are then uniutcrfered with. 

 1800. ji 



