CYCLIC MOLECULAR VARIATION 619 



by this consideration. I explained, in the first chapter of 

 the present work, the fact that the molecular derangement 

 of matter under stimulus might be studied by recording 

 any one of several concomitant physical changes. These 

 are : (a) the change of form contraction or expansion ; 

 (6) the electro-motive change ; and (V) the variation of electric 

 resistivity. By means of the first of these we investigated 

 the responsive effects induced by stimulus in animal and 

 vegetable tissues, and in the inorganic substance indiarubber. 

 By the second, that of electro-motive variation, the excitatory 

 change and its variations were studied in living tissues, animal 

 and vegetable, and in inorganic bodies like metal wires. 

 And, lastly, by variation of resistivity, we have obtained 

 records of excitatory changes in living tissues, as also in 

 masses consisting of metallic particles. In the last chapter, 

 moreover, I have shown that the molecular responses of a 

 magnetic substance may be recorded by means of appropriate 

 magnetometric or galvanometric methods. 



I shall now take up the question of the nature of those 

 obscure molecular modifications which the response of a 

 substance is found to undergo, and in consequence of which 

 it exhibits variations either of intensity or of sign. The 

 only conceivable reason for such changes would lie in some 

 unknown transformation of the antecedent molecular con- 

 dition. This being so, the next question is, whether we could 

 possibly discover what these transformations are. 



The properties of a substance at any given moment, we 

 must remember, are not determined solely by the nature of 

 that substance, but also by the energy which it possesses. 

 It is obvious, for instance, that the responsive properties of 

 matter, when its energy is depleted or its condition is a-tonic, 

 will be different from those of matter in a higher tonic con- 

 dition, and that there will be many gradations intermediate 

 between the two. Thus, as a substance is gradually trans- 

 formed, from a state of depletion to one of excessive energy, 

 we -can see that, theoretically, there might be two possible 

 ways of obtaining an insight into the progressive molecular 



