228 PHYSIOLOGY OF MUSCLES AND NERVES. 



2. Let us suppose, for example, that in the body 

 described in Chapter X. § 2, the distribution of the 

 tension which prevails on the surface as the result of 

 the electromotive forces then assumed, has been proved. 

 Let us now imagine that this particular electromotive 

 force is removed, and is replaced by another, situ- 

 ated at any other point in the body. Accordingly, the 

 body will be occupied by current-curves of different 

 form, corresponding with different iso-electric curves. 

 Consequently, the distribution of tension on the sur- 

 face is also quite different. A third electromotive 

 force situated at any other point would again involve 

 an entirely different distribution of the tension, and so 

 on. Helmholtz has shown that when many such 

 electric forces are present at one time in a body, the 

 tension which actually prevails at each point of the 

 surface is equal to the sum of all the tensions which 

 would be generated at this point by each of the electro- 

 motive forces by itself. If, therefore, a certain distri- 

 bution of tension has been experimentally found, it is 

 possible to conceive many combinations of electromotive 

 forces which might afford such a distribution of tension. 



The rules of scientific logic afford a standard by 

 which to choose to which of all these possible com- 

 binations- the preference shall be given. The theory 

 selected must, in the first place, be able to explain, not 

 only one, but all the circumstances experimentally 

 found. If new facts are discovered by new experi- 

 ments, then it must be able to explain these also, or it 

 must be relinquished in favour of a better theory. 

 Secondly, if several theories seem equally to satisfy the 

 required conditions, then preference must be given to 

 the simplest rather than to the more complex theories. 



