536 



MOVEMENTS. 



With the exception of the right auricle of the heart, the muscles of the voluntary sys- 

 tem were the last to lose their irritability. In one instance, certain of the voluntary 

 muscles that had not been exposed retained their contractility seven hours and fifty min- 

 utes after death. The observations of Longet and Masson show that a galvanic shock, 

 sufficiently powerful to produce death, instantly destroys the irritability of the muscular 

 tissue and of the motor nerves. 



One of the most important questions to determine with regard to muscular irritability 

 is whether it be a property inherent in the muscular tissue or derived from the nervous 

 system. The fact that muscles can be excited to more powerful and regular contractions 

 by stimulating the motor nerves than by operating directly upon their substance, and the 

 great difficulty in tracing the nerves to their termination in the muscles, have led to the 

 view that muscular contractility is dependent upon nervous influence, and consequently 

 that the muscles have no irritability or contractility, as a property inherent in their own 

 substance. This doctrine, however, cannot be sustained. 



The experiments of Longet, published in 1841, presented almost conclusive proof 

 of the independence of muscular irritability. He resected the facial nerve and found 

 that it ceased to respond to mechanical and galvanic stimulus, or, in other words, lost 

 its irritability, after the fourth day. Operating, however, upon the muscles supplied 

 exclusively with filaments from this nerve, he found that they responded promptly to 

 mechanical and galvanic irritation, and that they continued to contract, under stimu- 

 lation, for more than twelve weeks. In some farther experiments it was shown that, 

 while the contractility of the muscles could be seriously influenced through the ner- 

 vous system, this was effected only by modifications in their nutrition. When the 

 mixed nerves were divided, the nutrition of the muscles was generally disturbed ; and, 



although muscular irritability persisted for some time 

 after the nervous irritability had disappeared, it be- 

 came very much diminished at the end of six weeks. 

 These experiments are very striking and satisfactory; 

 but the whole question was definitively settled by the 

 observations of Bernard upon the peculiar influence of 

 the woorara-poison and the sulphocyanide of potas- 

 sium. As the result of these experiments, it was 

 ascertained that some varieties of woorara destroy 

 the irritability of the motor nerves, leaving the sen- 

 sitive filaments intact. If a frog be poisoned by intro- 

 ducing a little of this agent under the skin, irritation, 

 galvanic or mechanical, applied to an exposed nerve, 

 fails to produce the slightest muscular contraction ; but, 

 if the stimulus be applied directly to the muscles, they 

 will contract vigorously. In this way the nerves are, 

 as it were, dissected out from the muscles ; and the dis- 

 covery of an agent that will paralyze the nerves with- 

 out affecting the muscles affords conclusive proof that 

 the irritability of these two systems is entirely distinct. 

 If a frog be poisoned with sulphocyanide of potassium, 

 precisely the contrary effect will be observed ; that is, 

 the muscles will become insensible to excitation, while 

 the nervous system is unaffected. This fact may be 

 demonstrated by applying a tight ligature around the 

 body in the lumbar region, involving all the parts ex- 

 cept the lumbar nerves. If the poison be now intro- 

 duced beneath the skin of the parts above the ligature, the anterior parts only are affect- 

 ed, because the vascular communication with the posterior extremities is cut off. If the 



FIG. 158. Frog's legs prepared so as to 

 show the, effects of woorara. (Bernard.) 



Galvanization of the nerves in this animal, 

 which has been poisoned with woorara, 

 has no effect ; while galvanization applied 

 directly to the muscles (see dotted lii 

 produces contraction. 



Ines) 



