96 NERVOUS SYSTEM. 



attended with important structural changes in the nerve- 

 fibres. The tubes lose their normal appearance, and the 

 medullary matter becomes opaque and coagulates in large 

 drops. The axis-cylinder is not so much modified in struct- 

 ure, but it certainly loses its characteristic physiological 

 properties. 



The excitability of the motor nerves, according to the 

 observations of Longet, disappears in about four days after 

 resection. 1 Of course, in experiments upon this point, it is 

 necessary to excise a portion of the nerve to prevent reunion 

 of the divided extremities ; but when this is done, after the 

 fourth day, galvanization of the nerve will produce no con- 

 traction in the muscles, though the latter retain their con- 

 tractility, as may be shown by the application of direct irri- 

 tation. This loss of irritability is gradual, and continues, 

 whether the nerve be exposed and stimulated from time to 

 time or be left to itself ; and the loss of excitability pro- 

 gresses from the centres to the periphery. In the researches 

 of Longet on this subject, it was found that the lower por- 

 tion of the peduncles of the brain lost their irritability first ; 

 then the anterior columns of the cord, then the motor roots 

 of the nerves, and, last of all, the branches of the nerves 

 near their termination in the muscles. 



The sensibility of the sensory nerves disappears from 

 the periphery to the centres, as is shown in dying animals 

 and in experiments with ansesthetics. The sensibility is 

 lost, first in the terminal branches of the nerves, next in the 

 trunks and in the posterior roots of the spinal nerves, and 

 so on to the centres. 2 "We have often illustrated this fact in 

 experiments upon the roots of the spinal nerves and in sec- 

 tion of the large root of the fifth pair within the cranial 

 cavity. "When an animal is brought so completely under 

 ,the influence of ether that the operation of opening the spi- 

 nal canal may be performed without inflicting the slightest 



1 LONGET, Trade de physiologic, Paris, 1869, tome iii., p. 171. 



2 LONfiET, Op. tit., p. 175. 



