228 Buchanan 



of mechanical effect and frequency, so that I am inclined to agree with 

 Piper that the amount of the voluntary effort does not affect the response 

 fre(|uency, even though I find this to be so very far from constant. The 

 two records reproduced in fig. 5 were the third and the last, in both of 

 which the squeeze was maximal. 



When we come to compare the mechanical with the electrical effect of 

 a voluntary effort in different people, we find that the stronger mechani- 

 cal effect is by no means always accompanied by the stronger, or even by 

 the more regular, electrical effect. Thus the maximal reading of the 

 dynamometer produced by the person just referred to as giving the strongest 

 and most regular electrical response was 21, and on most occasions when 

 he was trjang to do his utmost the reading fell short of this and was only 

 18, 19, or 20. Almost immediately afterwards the experiment was repeated 

 (with exactly the same recording arrangements) with the flexores digitorum 

 of another subject who brought the reading up to 83 while the electrical 

 response was being recorded. The records showed that the separate 

 excursions of the meniscus were less strong (ascents less steep) and also 

 less regular, although more regular than in a good many people. It would, 

 I think, be premature to do more than call attention to this fact at the 

 present moment. It is illustrated by a comparison of figs. 4 and 6 A with 

 fig. 5 A, the scale reading 25 with each of the two people whose flexors gave 

 figs. 4 and 6 A. So far as the strength of the electrical efl'ect is concerned, 

 since we know that in the same person this varies with the strength of 

 the mechanical efl'ect, we must look to something outside the muscle and 

 the voluntary eflbrt to account for the differences in different people. 

 Variation in conductivity of tissue (fat and skin) interposed between muscle 

 and electrodes is what first suggests itself, but I have as yet made no 

 attempt to measure this. 



IV. Contrast between the Capillary Electrometer Record of 

 THE Voluntary Response and that of the same Muscle to 

 Artificial Excitation of its Nerve by a Series of Induction 

 Shocks of a Frequency of about 50 per second. 



Below the record (tig. 6 A) given by the flexor muscle in response to the 

 will there is reproduced (flg. 6 B) the record (on a plate moving at the same 

 rate) given by the very same muscle immediately before (when the leading- 

 ofl' electrodes and the surface to which they were applied were precisely 

 the same) in response to a series of induction shocks applied to the skin 

 over the median nerve where it comes nearest to the surface just under 

 the lower end of the biceps. The artificial stimulus was supplied by 

 the vibrator of a Kronecker inductorium with secondary coil right up 

 and no core in the primary coil. It produced a strong sensation. 

 Contact was made and then broken 44 times a second. Whereas the 

 subject was exerting himself in order so to compress the steel ellipse that 



