62O COMPARATIVE ELECTRO-PHYSIOLOGY 



changes occurring in it. First of these would be the con- 

 tinuous observation of the character of the replies made by 

 the changing substance to the shock of stimulus, with the 

 progressive modification of those replies. And the second 

 method would lie in taking a continuous record of some 

 property of the substance, as a whole, which was undergoing 

 a concomitant change. In the first of these modes of 

 scrutiny the information would be obtained by an inspec- 

 tion of the varying responses. In the second, it would be 

 arrived at by the examination of certain characteristic curves ; 



FIG. 378. Characteristic Curve of Iron under increasing Force of 

 Magnetisation 



and finally, if both these methods gave correct indications of 

 the molecular state at the time being, then each particular 

 response of the first method would be found to have its 

 own place in the characteristic curve of the second. This 

 characteristic curve will be best understood from a con- 

 tinuous record of the induced molecular change occurring 

 under the action of an increasing external force. The 

 simplest example of this is afforded by the curve which 

 shows the relation between induced magnetisation and 

 inducing magnetic force (fig. 378). This induced magne- 

 tisation, as will be understood, measures the amount of 

 molecular distortion. A characteristic curve, essentially 



