396 BIOLOGY, [Book vi. 



If we are still ignorant as to what the molecfular vibration, 

 formerly called nervous influx, is, in its essence, we are not better 

 instructed as to the manner in which this vibration is transmitted 

 to the contractile muscular elements. By what mechanism do 

 the dissociated nervous fibres, divested of their protecting 

 envelopment, when they are insinuated between the muscular 

 fibres of the animal life, between the fibro-cells of the 

 sanguineous vessels and the apparatus of nutritive life, succeed 

 in modifying the state of these elements, determining their 

 contraction, and that with much greater energy than would be 

 exercised by an excitation bearing upon the contractile element 

 itself? One more unsolved problem to be added to so many 

 others. 



In most questions relating to the method in which the nervous 

 tissues live and act, we must therefore content ourselves with 

 recording plain facts, of which we are unable to give any satis- 

 factory explanation. If physiologists are unable to tell us why 

 the nervous cell excites the motoiy fibre, how the latter 

 tiunsmits this excitation to the muscular fibre, neither can 

 they explain how curar6 specially kills the motory nervous fibre, 

 sparing the sensitive fibre. Certainly we have here a fresh proof 

 of radical diversity between these two orders of nervous 

 conductors. 



The wourara, or curar^ of which the South American Indians 

 make use to poison their arrows, has, in fact, the very curious 

 property of selecting, to some extent, the motory nervous fibres. 

 Once introduced into the circulatory system of any vertebrated 

 animal, in a veiy small quantity, it strikes with paralysis the 

 •whole of the motory network, leaving perfectly unimpaired the 

 whole of the sensitive network. Its action is first disclosed by 

 slight convulsive movements, followed by the progressive extinc- 

 tion of all the movements of the life of relation. The effect of 

 curar^ whilst more manifest and prompt in vertebrated animals, 

 nevertheless is not peculiar to them. In fact, curare also acts 

 upon the aquatic larvae of insects, upon naids, and moUusks, 



