CYCLIC MOLECULAR VARIATION 



necessarily set up, by which material in one part may be 

 accreted, and in another dissolved. In this way a positive 

 or negative image may be developed. 



We have also seen, in the responses of living tissues, that 

 while moderate stimulation induces one effect, the same 

 stimulation, long continued, may cause the so-called fatigue- 

 reversal, such reversals sometimes, in fact, becoming 

 recurrent. It is interesting to note that in a similar fashion 

 a photographic plate, subjected to various durations of 

 exposure, will give either negative or reversed positive 

 images, or recurrences of these. 1 



From such facts it is clear that for the elucidation of 

 response and its variations, we must look to its molecular 

 antecedents, and not to its secondary chemical or other 

 consequences. If response phenomena in general, then, are 

 determined by molecular conditions, as such, it follows that 

 in order to unravel the anomalies which occur in the 

 response of living tissues, we must attempt to ascertain those 

 conditions vyhich induce any given variation of response in 

 matter in general. That these phenomena are not peculiar 

 to the response of living tissues, but take place in all matter 

 under similar circumstances, is a fact which has been often 

 reiterated in the course of previous chapters, and which I 

 first pointed out in the course of my investigations on 

 * Response in the Living and Non-Living.' 2 



In the work in question, referring to the occurrence of 

 abnormalities in response, I said : 



' Calling all normal response negative, for the sake of 

 convenience, we observe its gradual modification, correspond- 

 ing to changes in the molecular condition of the substance. 

 Beginning with that case in which molecular modification is 

 extreme, we find a maximum variation of response from the 

 normal, that is to say, to positive. Continued stimulation, 

 however, brings the molecular condition to normal, as 



1 Bose, ' On Strain Theory of Photographic Action,' Proc. Roy. Soc. 

 1902. 



See Response in the Living and Non- Living (1902), pp. 129, 130. 



