110 THE NATURE OF THE 



closely investigated by physiologists. Hitter, as is well known, 

 first maintained that there is a special law of contraction for the 

 thigh of the frog as a whole, and called attention to a difference 

 with respect to excitation between the flexors and extensors. 



The truth of this much-questioned assertion of difference in 

 excitability between physiologically different groups of muscles was 

 established by R-ollet, and is confirmed by recent investigations of 

 my own, which will shortly be published. This difference manifests 

 itself at closure and opening in the fact that the more powerful 

 stimulus affects the less excitable extensors most, while the weaker 

 stimulus has most effect on the more excitable flexors. Thus, if one 

 applies a pair of either polarisable or unpolarisable electrodes to 

 the sciatic nerve of a frog at a point midway between its point of 

 exit from the spinal cord and the point where it disappears in 

 the thigh, care being taken that they are kept in exactly the 

 same position, it will not be observed that as the strength of the 

 currents employed is raised the same group of muscles merely con- 

 tract more and more strongly, but that quite different muscles con- 

 tract with weak and strong currents respectively x . If one carefully 

 observes which muscles first contract at closure of weak currents 

 (usually certain muscles of the thigh and toes), the interesting fact 

 will be observed that on further increase of the current-strength 

 other muscles are excited, and always more and more strongly at 

 closure, while at opening those muscles alone contract which had 

 previously contracted with weak currents at closure. The break- 

 excitations of these relatively strong currents are now similar in 

 their effect to make-excitations of the weak currents. 



Similar phenomena occur in human muscles, and I am astonished 

 to find no mention of them in handbooks of electro-therapeutics. 

 For instance, if with a sufficiently strong current the electrodes are 

 placed a few centimetres apart in the groove on the inside of the 

 biceps, it will be observed constantly that with certain current- 

 strengths other muscles contract at closure than at opening. I 

 often noticed strong flexion of the hand on closure, and moderate 

 pronation on opening the same current. 



In experiments on man (which I have only made cursorily, and 

 intend to pursue further when I have an opportunity) the conditions 

 are of course not so apparent as in the case of separated frogs' nerves. 

 It can be more particularly objected that if the electrodes are 

 sufficiently far apart the points of excitation are also far apart, and 

 1 See the dissertation of L. Nemerowsky, Berne, 1883. 



