MUSCULAR CONTRACTILITY, OR EXCITABILITY. 



473 



In the human subject and the warm-blooded animals, the muscles cease 

 to respond to a stimulus a few hours after death, although the time of dis- 

 appearance of excitability is very variable. Nysten, in a number of experi- 

 ments upon the disappearance of excitability in the human subject after de- 

 capitation, found that different parts lost their contractility at different peri- 

 ods, but that generally this depended upon exposure to the air. AVith the 

 exception of the right auricle of the heart, the striated muscles were the last 

 to lose their excitability. In one instance, certain of the voluntary muscles 

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

 minutes after death. Longet and Masson found that an electric shock, suf- 

 ficiently powerful to produce death instantly, destroyed the excitability of 

 the muscular tissue and of the motor nerves. 



The experiments of Longet (1841) presented almost conclusive proof of 

 the independence of muscular excitability. He resected the facial nerve and 

 found that it ceased to respond to mechanical and electric stimulus, or in 

 other words, lost its excitability, after the fourth day. Operating, however, 

 upon the muscles supplied exclusively with filaments from this nerve, he 

 found that they responded promptly to me- 

 chanical and electric stimulation, and that 

 this continued for more than twelve weeks. 

 In other experiments it was shown that while 

 the contractility of the muscles could be seri- 

 ously influenced through the nervous system, 

 this was effected only by modifications in their 

 nutrition. When the mixed nerves were di- 

 vided, the nutrition of the muscles was gener- 

 ally disturbed; and although muscular con- 

 tractility persisted for some time after the 

 nervous excitability had disappeared, it be- 

 came very much diminished at the end of six 

 weeks. Some varieties of curare destroy the 

 excitability of the motor nerves, leaving the 

 sensitory filaments intact. If a frog be poi- 

 soned by introducing a little of this agent 

 under the skin, stimulation, electric or me- 

 chanical, applied to an exposed nerve, fails to 



produce muscular Contraction : but if the FlG - 154 - Frog's legs prepared so as to 



. . show the effects of euro re (Bernard). 



Stimulus be applied directly to the muscles, Faradization of the nerves in this ani- 



i] , T ,-, . ,, mal, which has been poisoned with 



tliey Will Contract Vigorously. In this Way the curare, has no effect ; while the 



i j- L ^ j. j-i stimulus applied directly to the 



nenes are, as it were, dissected out from the muscles (see dotted lines) produces 

 muscles ; and the discovery of an agent that contraction, 

 will paralyze the nerves without affecting the muscles affords conclusive 

 proof that the excitability of these two systems is distinct. If a frog be 

 poisoned with potassium sulphocyanide, precisely the contrary effect is ob- 

 served ; that is, the muscles will become insensible to excitation, while the 

 nervous system is unaffected. This fact may be demonstrated by apply- 



