ANIMAL AND VEGETABLE 83 



point is taken to be positive to the latter ; and, vice versd, 

 the lower is taken to be negative to the higher point. The 

 terms positive and negative currents are frequently used, 

 but they are misnomers. There is only one current 

 flowing and it varies in direction. It is quite correct to 

 apply the term positive or negative to currents with respect 

 to a given point, and by those terms to imply direction only, 

 for while stationed at a given place currents may flow from 

 or towards us ; but what is a positive current at one point 

 is a negative current at another. ... A current can only 

 be constant when we have two points separated from each 

 other by an invariable resistance, and maintained at the 

 same difference of potential." 



We shall see, later on, that in the human body neither 

 the resistance of any given circuit nor the same difference 

 of potential can be maintained owing, quite apart from 

 disease, to variations of external temperature and the 

 fluctuating nature of the human electromotive force ; 

 and the fact is emphasised that in the estimation of body 

 deflections we must have a fixed point of departure, and 

 that that point should be upon the central line. 



We will now consider Dr. Martin's letter upon " The 

 Source of Body Energy and its Relation to the Nervous 

 System." 



He says : " The theory of neuro- electricity, gal- 

 vanometric tests, and treatment, founded upon the theory 

 propounded by Mr. Baines, has proved of value in the 

 treatment of certain conditions of disease. The argument, 

 therefore, follows that the basis of the theory is sound. 

 In detail, however, the original conception of the brain 

 as a generator, and the nervous system as a carrier, of a 

 constant current came into collision with established 

 physiology, and endangered the hearing of a piece of 

 scientific work of great value. 



" I advance a theory which may bean explanation, and 



