224 Buchanan 



This means that it is difficult to find any place on the arm which, 

 to judge from the records, remains wholly electrically inactive when 

 the fist is clenched. I tried to do this by varying the position of 

 the second leading-off electrode, leaving the one applied to the 

 most active part of the flexors and connected with the acid of the 

 electrometer, in the same position. Records were always first taken 

 with the second electrode on the skin over the tendons of the flexors 

 near the wrist (position i.). It was then sometimes moved so as to 

 be also on the contracting muscle at a place about 10 cm. distal to 

 the other electrode, i.e. presumably on a spot of nearly the same 

 activity (position ii.); or it was placed (iii.) either on the back of the 

 elbow or on the shoulder, i.e. on a spot likely to remain inactive when 

 the flexors contracted. So long as the two electrodes made contact 

 with equal areas of the skin, the records taken with the second one 

 in positions i. and iii. gave as little evidence that the effect represented 

 related to what was happening under the first electrode only, as did those 

 taken with it in position ii. The amplitudes of the excursions were, how- 

 ever, less when the second electrode was in position ii. than when it was in 

 position i. It was in position i., in the records reproduced in figs 4, 5, 

 and 6. There is, so far as I can see, no way of assuring oneself of the 

 neutrality of any particular spot in the arm of a living person while it is 

 performing any voluntary action. It would be easier to assure oneself of 

 the neutrality of some quite other part of the body so far as mechanical 

 action is concerned, but no other part of the body save the limb to 

 which the fixed electrode is attached will serve the purpose when it is 

 the electrical action which is concerned, because the changes due to the 

 heart's electrical action are apt to appear whenever the two electrodes 

 are far apart on the body and add further complication to the record 

 (see note on p. 241). 



By reducing the size of the area of contact made with the 

 second electrode I have, how^ever, obtained records which, to anyone 

 accustomed to the interpretation of them, would suggest that the spot under 

 one electrode was recording alone, or to a much larger extent than the 

 other. Fig. 5 shows the records of the voluntary response given by 

 the flexors when, on tlie one hand (A), tlie two electrodes (in position i.) 

 were each 3 to 4 cm. in diameter ; and when, on the other (B), the one of them 

 (that connected with the mercury) was reduced so that it made contact 

 only with an area of skin Ii cm. in diameter. The rounded summits of 

 the individual excursions in B contrast strongly with the pointed summits 

 in A. The capillary electrometer shows the same sort of difference between 

 the action currents (Einzelschwankung) of a frog's sartorius when, on the 

 one hand, the tendon end (connected with the mercury) is devitalised, and 

 when, on the other, it is sound. 



All the records furnished by the flexors of the same individual as those 

 reproduced in fig. 5 were far more regular than were those supplied by any 



