72 ELECTRO-PHYSIOLOGY CHAP. 



regards the dependence of a reflex twitch upon strength of excita- 

 tion, it should be remarked that it is only within a very narrow 

 range of stimuli that magnitude of contraction increases with that 

 of stimulation. Directly the stimulus is capable of discharging 

 any reflex it provokes a fairly strong twitch of the muscle, which 

 cannot be much increased by further augmentation of stimulus : 

 the reflex time, on the other hand, is diminished. Accord- 

 ing to Eosenthal (31), the reflex time may be so reduced with 

 strong excitation that nothing remains of Helmholtz's phenomenon, 

 and if the time which the excitation takes to travel from the 

 point stimulated to the spinal cord, and thence to the muscle, is 

 calculated, the sum of botli will be approximately equal to the 

 latent period as measured. The limited range within which 

 increment of stimulus produces perceptible increase of reflex 

 action diminishes with stronger doses of the poison, and finally 

 vanishes (Eosenthal). 



The phenomena exhibited by strychninised frogs are very 

 characteristic. In normal reflexes the least stimulus applied to 

 the hind foot induces flexion of the corresponding leg, while the 

 extensor muscles remain quiescent. The action after strychnin 

 poisoning is quite different ; there is always pronounced contrac- 

 tion of all the muscles of the leg, and the extensors being the 

 most powerful, the limb is stretched out convulsively. It is a 

 question how the normal co-ordinated flexor reflex is converted 

 after strychnin poisoning into the uncoordinated reflex of exten- 

 sion. If the normal dose is much reduced ( = 0'0001 gr.) it 

 will be found insufficient to transform the flexor into the extensor 

 reflex, though there is still some effect on the spinal medulla, 

 since a weaker stimulus provokes the reflex, and the reflexes 

 appear more promptly and inevitably. As soon as these minute 

 doses are exceeded, the spasmodic extension reflex sets in. While 

 in the co-ordinated flexor reflex certain definite paths are alone 

 excited, in the uncoordinated reflexes of extension all are 

 excited simultaneously, and the extensors, as the more active, 

 determine the movement of the limb. If the spinal cord is 

 sufficiently strychninised there is a simultaneous contraction of 

 all the skeletal muscles, discharged from every possible point of 

 active sensory excitation as though all the corresponding nerves 

 were caught into a bundle and excited at the same moment. But 

 if it is possible, under the action of strychnin, thus to excite all 



