124 THE SIGNS OF LIFE [LECT. 



sensations, intellectual effort, or strained attention bring about 

 similar effects "always, of course, during complete immobility 

 of the subject." Voluntary movement of any part of the body, 

 during absolute quiescence of the part connected with the 

 galvanometer, gives a skin current the strength of which is 

 dependent on the strength of the voluntary effort. He says 

 that parts in which sweat-glands are most abundant (palm of 

 hand, toes, axilla, etc.) become negative to parts containing few 

 glands (back, nates, external surface of thigh and arm), and 

 considers, therefore, that the active state of the nervous system 

 gives rise to an ingoing secretion current similar to that shown 

 by Hermann in the case of the frog's skin, by excitation of its 

 cutaneous nerves. 



Tarchanoff further assures us that he used a sensitive, almost 

 completely aperiodic, galvanometer, giving with the nerve cur- 

 rent of a frog's sciatic a deflection " off scale " (i.e., greater than 

 50 divisions) ; the skin effects he observed also gave deflections 

 " off scale," had a latent period of one to three seconds, outlasted 

 the stimulus by several minutes, and returned gradually but 

 irregularly to rest. Connection with the skin was made from 

 unpolarisable electrodes of the usual type by strips of hygro- 

 scopic wool (10 to 15 cm. long) soaked in normal saline, brought 

 in contact with pads of the same material previously applied to 

 the skin. These pads were of an area of 10 to 15 cm. The 

 currents of rest were previously compensated. In the case of 

 the hand, the effect of gentle tickling was generally such 

 that "die Basis der Finger in der Mehrzahl der Falle nega- 

 tive, der Thenar dagegen positive elektrische Spannung 

 besitzt." Imaginary sensation gave deflections of 10 to 15 

 divisions. 



Now these things are clearly of considerable interest, if a 

 true physiological effect regularly coincident with nervous 

 activity can be demonstrated ; and I have somewhat minutely 

 described to you the conditions of observation, in case any one 

 should be inclined to make fair and patient test of the state- 

 ments. I must confess, however, that for my own part I am not 

 convinced that the deflections have been anything more than 

 rather unduly pronounced galvanometric vagaries occurring 



