INDEPENDENCE OF MUSCULAR IRRITABILITY. 825 



it next to certain that their ordinary operations are not dependent upon any 

 stimuli received through the nerves, but upon those directly applied to them- 

 selves. 4. The persistence of irritability in muscles, for some time after the 

 nerves have ceased to be able to convey to them the effects of stimuli ; this 

 is coustautly seen in regard to the Sympathetic system of nerves, and the 

 muscles of organic life upon which they operate; and it is shown, by the 

 agency of narcotics, to be true also with respect to the Cerebro-spinal sys- 

 tem and the muscles of Animal life. 5. The continuance of irritability in 

 the muscles after their complete isolation from the nervous centres, so long 

 as their nutrition is unimpaired ; and the effects of frequent exercise in pre- 

 venting the impairment of the nutrition and the loss of irritability. 6. The 

 recovery of the irritability of muscle, when isolated from the nervous cen- 

 tres, after it has been exhausted by repeated stimulation : this also depends 

 upon the healthy performance of the nutritive actions. 7. The existence of 

 certain poisons which appear to possess a directly depressing effect on the 

 conducting power of motor nerves, without exerting any influence upon the 

 irritability of muscles ( 670). 8. The existence of certain tracts of mus- 

 cular tissue, as those, for instance, of the walls of the umbilical vessels, 

 which, according to Virchow, whilst possessing considerable irritability, show 

 no trace of nervous tissue. In the words of Dr. Alison, then, " the only 

 ascertained final cause of all endowments bestowed on nerves in relation to 

 muscles in the living body, appears to be not to make muscles irritable, but 

 to subject their irritability in different ways to the dominion of the acts and 

 feelings of the mind " to its volitions, emotions, and instinctive determina- 

 tions. 1 



675. There can be no question that the condition most essential to the 

 maintenance of muscular contractility is an adequate supply of arterial blood. 

 It is well known that when a ligature is applied to a large arterial trunk in 

 the Human subject, there is not only a deficiency of sensibility in the surface,, 

 but also a partial or complete suspension of muscular power, until the col- 

 lateral circulation is established. The same result has been constantly 

 attained in experiments upon the lower animals ; the contractility of the 

 muscle being impaired or altogether extinguished when the flow of blood 

 into it was arrested, and being recovered again when the supply of blood < 

 was restored. The various experiments of M. Brown-Sequard 2 on this sub- 

 ject are still more satisfactory, as showing that the contractility of muscles,. 

 whether of the striated or smooth variety, may not only be restored by the 

 transmission of aerated blood through them, after it has entirely ceased, but 

 that this may even occur when it has given place to cadaveric rigidity. 

 Thus he found that when he connected the aorta and vena cava of the body 

 of a rabbit which had been some time dead, and in which the cadaveric 

 rigidity had already manifested itself for between ten and twenty minutes, 

 with the corresponding vessels of a living rabbit, so as to re-establish the 

 circulation in the lower extremities, the rigidity disappeared in from six to 

 ten minutes, and in two or three minutes afterwards the muscles contracted 

 on being stimulated. He subsequently made similar experiments upon the 

 muscles of a decapitated criminal ; the hand being selected as a convenient 

 part for the purpose. It was not until nearly 12^ hours after death that all; 

 traces of irritability had left the muscles, and the injection was not 



1 For a good resume of the arguments for and against the theory of independent 

 irritability in muscles, see a paper by Dr. H. N. Maclaurin in Edinb. Med. Journal, 

 July, 1863. 



2 "See Gazette Me'dicale, 1851, Nos. 24 and 27; and Journal de laPhysiologie, 1858, 

 vol. i, pp. 95, 353, 729. For some more recent experiments, see M. Kobin in his 

 Journal de 1'Anatomie, 1869, p. 69. 



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