INHERENT IRRITABILITY OF MUSCULAR FIBRE. 447 



served by Dr. M. Hall, and heretofore adverted to ( 399), that in cases in which the 

 cause of the paralysis is situated in the Brain, and in which the Spinal Cord and its 

 nerves are unaiiivtcd, the irritability of the muscles of the paralyzed part is not destroyed, 

 even after a considerable lapse of time. For, if the capability of performing reflex actions 

 still exist, on the part of the nervous system, it is manifest that the muscles will be < 

 sionally excited to action through this channel; and that their nutrition and vital prop*-, 

 will thereby be preserved, as they were in Dr. Reid's experiments by the artificial excite- 

 ment of galvanism. Hence Dr. M. Hall's opinion, that the property of Muscular contrac- 

 tility is derived from the Spinal Cord, is no more tenable than that which locates it in the 

 Brain. 



c. The loss of irritability from section of the nerves, takes place more speedily in warm- 

 blooded Vertebrata, all whose vital operations are performed with a much greater activity, 

 than in Reptiles, and other cold-blooded animals. Dr. Reid found that, in a Rabbit, a por- 

 tion of whose sciatic nerve had been removed on one side, the muscles of that leg were but 

 very feebly excited to contraction by Galvanism, after the lapse of seven weeks. The change 

 in their nutrition was evident to the eye, and was made equally apparent by the balance. 

 The muscles of the paralyzed limb were much smaller, paler, and softer, than the corre- 

 sponding muscles of the opposite leg; and they scarcely weighed more than half, being 

 only 170 grains, whilst the others were 327 grains. It was found, also, that a perceptible 

 difference existed in the size of the bones of the leg, even after so short an interval had 

 elapsed; the tibia and fibula of the paralyzed limb weighing only 81 grains, whilst those of 

 the sound limb weighed 89 grains. On examining the muscular fibres with the microscope, 

 it was found that those of the paralyzed leg were considerably smaller than those of the 

 sound limb, and presented a somewhat shrivelled appearance; and that the longitudinal and 

 transverse stria? were much less distinct. 



d. Another equally satisfactory proof, that the loss of Irritability, which follows the sever- 

 ance of the connection between the Nervous centres and the Muscle, is not immediately due 

 to the interruption of any influence communicated by the former, has been given by the ex- 

 periments of Dr. J. Reid. He has proved, that if the irritability of Muscles be exhausted by 

 means, which have no tendency to impair their healthy nutrition, and the other conditions 

 favour the normal performance of the nutrient processes, the irritability is restored, and re- 

 mains for some time. His first experiments were on cold-blooded animals, and they would 

 in themselves be sufficiently satisfactory ; but he has since repeated them in the Rabbit, and 

 established the fact beyond all doubt.* " The sciatic nerve was divided in the Rabbit, 

 and a portion of it removed. One wire from two galvanic batteries consisting of thirty 

 pairs of plates, was applied over the course of the nerve ; and the other wire was applied 

 over the foot, which was kept moist, until the muscles had ceased to contract. Three 

 days after this, a weaker battery was used, and the muscles of the limb had recovered 

 their contractility, and contracted powerfully. The more powerful battery was used as 

 before, until the muscles had ceased to respond to the excitement; and three days after 

 this, they had again recovered their contractility." It seems scarcely possible to draw any 

 other inference from these experiments, than that Irritability is a property inherent in Mus- 

 cular tissue, and that the agency of the Nervous system upon it is merely to call it into 

 active operation. 







590. The second doctrine referred to, as having been taught by some Phy- 

 siologists, is, that Muscles, though not dependent on nerves for their peculiar 

 vital power, are yet dependent upon them for the exercise of that power; 

 all stimuli, which excite muscles to contraction, operating first on the nervous 

 filaments which enter muscles, and through them on the muscular fibres. 



a. The facts which have been already stated, in regard to the ordinary action of the Mus- 

 cles of Organic life, furnish a sufficient answer to this hypothesis. It is with great difficulty 

 that these can be made to display their irritability, by any stimuli applied to their nerves ; 

 whilst they manifest it strongly, when the stimulus is directly applied to themselves. Even 

 in the Muscles of Animal life, individual fasciculi may be thrown into action in the same 

 manner; although the entire mass cannot be put into combined operation, except by a stimu- 

 lus simultaneously communicated to the whole, which the nerve affords the readiest means 

 of effecting. Perhaps the most satisfactory disproof of it, however, is to be found in the ob- 



the other ; so that there was a difference of more than an inch in the circumference of the 

 limbs. But since the paraplegia has been recovered from, voluntary power having been es- 

 tablished in both limbs, and the muscles of both having been exercised in the same degree, 

 they have greatly improved in size and firmness, and there is no lon-rer any perceptibl'/ 

 ference between them. * L OC . c it. 



