4 PHYSIOLOGY CHAP. 



In 1841, Longet resorted to a very simple method of deciding 

 the question, by cutting the nerves to a limb of a mammal, and 

 testing the direct and indirect excitability of its muscles, at 

 various intervals after the operation. He found that the nerves 

 lost their excitability to all stimuli (mechanical, chemical, 

 electrical) after the fourth day ; while the muscles to which these 

 nerves were distributed reacted to direct stimulation as long as 

 twelve weeks after the operation. To this argument in favour 

 of autonomous muscular excitability it was objected that the 

 degeneration and loss of excitability in the nerve is propagated in 

 a centrifugal direction, i.e. from the point of section towards the 

 nerve-endings, and that the end-plates might consequently retain 

 their excitability after total degeneration of the corresponding 

 fibres. Microscopical investigation, however, shows that the small 

 muscular nerves are already altered eight to ten days after the 

 section, and it would therefore be illogical to suppose that the 

 end-plates can remain intact several months longer. Clinical ob- 

 servations confirm this fact ; the muscles of the face, for instance, 

 preserve their direct excitability several years after the facial 

 nerve has been paralysed (C. Richet). 



Another more effective method of showing that muscular 

 excitability is independent of the corresponding nerves was dis- 

 covered in 1850 by Cl. Bernard, and almost simultaneously by 

 Ko'lliker. The strongest stimuli applied to the nerves of 

 animals paralysed by curare are unable to excite any contraction 

 of the skeletal muscles ; but the muscles preserve their direct 

 excitability. Curare neither paralyses the sensory nerves nor 

 the nerve-centres, its paralysing action being limited (except 

 with excessive doses) to the motor nerve -endings. In fact, if 

 the sciatic nerve of a frog is exposed on the right side, and that 

 leg, leaving out the sciatic, is ligatured, and curare is then injected 

 under the skin of the back, the right leg reacts when its sciatic 

 nerve is stimulated ; but when the left sciatic is stimulated no 

 reaction of the muscles on that side is obtained because the poison 

 has been circulating through them, while there are reflex move- 

 ments from the right leg. The section of a motor nerve abolishes 

 excitability from the point of section to the periphery, but the 

 toxic action of curare begins by paralysing the motor end-plates, 

 and then extends centripetally along the nerve. Curare does not 

 therefore alter the excitability of the muscle perceptibly (at any 

 rate in small doses and in the early stages of its action), but it 

 paralyses motor nerves, by abolishing the conductivity of the motor 

 end-plates, and thus interrupts the normal link between the nerve 

 and its muscle. 



A simpler and no less conclusive argument was brought 

 forward by Kiihne (1859). He observed that the sartorius muscle 

 of the frog has no nerve fibres near its end, for about ^ of its 



