82 STUDIES IN ELECTRO-PHYSIOLOGY: 



upon the electromotive force of the cells used.* In the tests 

 to which reference has been made the electromotive force 

 was 20 volts. The average electromotive force of man 

 may be put at a maximum of 5 millivolts, so that the 

 quantity of the charge with 20,000 millivolts would be 

 many times greater than with 5 millivolts, and this, I 

 think, suggests (1) that although the insulating processes 

 of the body are not adapted to withstand the strain of 

 high tension (and capacity is regarded as a strain upon the 

 dielectric), they are adequate for the purposes for which 

 they were designed ; (2) that the body can be inductively 

 influenced by any outside source of electrical energy of a 

 potential appreciably higher than 5 millivolts ; and (3) 

 that as the quantity of current exhibited by a healthy man 

 may be expressed as being less than 1 micro-ampere, we 

 are justified in assuming that the law of retardation applies 

 with equal force to the human organism. 



In the elaboration of my theory of the nature of the 

 nerve impulse, i.e., that it is neuro- electrical and due to 

 the association of iron as the positive and oxygen as the 

 negative element, in the presence of an exciting liquid, I 

 was confronted by the fact that I could not, as an elec- 

 trician, recognise or point to any organ in the body which 

 could be said to be a generating station. I am indebted for 

 what may be the missing link to a communication from 

 Dr. E. W. Martin, from which I shall presently take the 

 liberty to quote. Before doing so, however, it may serve 

 a useful purpose as this work is intended for the guidance 

 of those who are not familiar with applied electricity to 

 offer a few observations upon so-called positive and negative 

 currents ; my authority being the text-book of Telegraphy, 

 by Preece and Sivewright. 



u A current is always supposed to flow from the point 

 of higher potential to that of lower potential. The former 

 * See also p. 91 et seq. 



