4:66 MOVEMENTS. 



taneous action of all the fibres of a muscle, or set of muscles ; 

 but galvanic, mechanical, or chemical irritation of the mus- 

 cles themselves will produce contraction, after the nervous 

 irritability has been abolished. 



The conditions under which muscular irritability exists 

 are simply those of normal nutrition of the muscular tissue. 

 When the muscles have become profoundly affected in their 

 nutrition, as the result of section of the mixed nerves, or after 

 prolonged paralysis, the irritability disappears and cannot 

 be restored. The determination of the presence or absence 

 of muscular contractility, in cases of paralysis, is one of the 

 methods of ascertaining whether treatment directed to the 

 restoration of the nervous power will be likely to be followed 

 by favorable results. If the muscular irritability have en- 

 tirely disappeared, it is almost useless to attempt to restore 

 the functions of the part. 



A great many experiments have been made upon the in- 

 fluence of the circulation on muscular irritability, chiefly 

 with reference to the effects of tying large vessels. Among 

 the most recent are those of Longet. He tied the abdominal 

 aorta in five dogs, and found that voluntary motion ceased 

 in about a quarter of an hour, and that the muscular irrita- 

 bility was extinct in two hours and a quarter. When the 

 blood was restored, after three or four hours, by removing the 

 ligature, the irritability and finally voluntary movement re- 

 turned. 1 These experiments show that the circulation of the 

 blood is necessary to the contractility of the muscles. Tying 

 the vena cava did not affect the irritability of the muscles. 

 In dogs in which this experiment was performed, the lower 

 extremities preserved their contractility, and the voluntary 

 movements were unaffected up to the time of death, which 

 took place in twenty-six hours. 3 



The relations of muscular irritability to the circulation 

 have been further illustrated, in some very curious and in- 



1 LONGET, Traite de physiologic, Paris, 1869, tome ii., p. 616. 



2 LONGET, op. tit., p. 618. 



