240 Buchanan 



the mechanical effect depends for its strength not so much on the strength 

 of the stinnikis as on its duration. An artificial instantaneous stimulus or 

 each of a series of such produces a greater electrical variation than is, in 

 the same muscle of the same person, produced by a central stimulus, but it 

 lasts so much shorter a time that it is unable to efiect what a more pro- 

 lono-ed, even though weaker, stimulus may do. In this connection I was 

 interested to learn recently from Dr Waller that he had long ago recorded 

 the reflex mechanical efiect of the extensors of the leg in man to a single 

 instantaneous stinuilu.s to the nerve, and that he had found it to be much 

 stronger in proportion to the direct effect than my records show to be the 

 case for the reflex electrical effect. 



VII. Summary. 



In the electrical response of human muscles to their normal stimulus a 

 rhythm presents itself which for the f lexores digitorum has no constant 

 frequency but may vary during one and the same response between 50 and 

 about 120 per second, but which for the masseters is more uniform and 

 of a higher frequency (170 to 200 per second). 



This rhythm is to be regarded as of peripheral origin, because it is of 

 the same order and subject to the same sort of variation as is a rhythm 

 which experiments on frogs have proved to be of such origin. 



As the corresponding rhythm may be produced in the response of frogs' 

 muscle to various kinds of artificial stimuli which are not discontinuous, 

 the rhythm obtaining in the electrical response of human muscle to the 

 will has as yet given us no information as to whether the natural stimulus 

 is rhythmical. Such information can only be gained by further experiments 

 upon animals (not only upon cold-blooded, but on warm-blooded ones), in 

 which it is possible to simplify and control the conditions to a greater 

 extent than is possible in man. 



VIII. Note on the Effect ox the Electrocardiogram of the 

 Contraction of the Voluntary Muscles in Man. 



If, while the electrocardiogram is being inscribed by the meniscus of the 

 capillary electrometer, the subject having his two hands in two basins of 

 salt solution connected with the two terminals, the one fist is clenched, a 

 number of line teeth appear on the curve which before was smooth, both 

 on that part of it which corresponds to the systole and on that which 

 corresponds to the diastole. It was the observation of this effect which 

 suggested the experiments on arm muscles described in this paper. The 

 teeth do not appear when muscles of other parts of the body alone are 

 put into action. They have a frequency of from 100 to 140 per second, 

 which I take therefore to be that of the electrical response of the muscles of 

 the hand. But there is another effect produced by clenching one fist on 

 the electrocardiogram which is equally striking, namely, the sudden and 



