CHAPTER II. 



What constitutes Normality in Structure and Environment — Definition of 

 Health— Test of Healthy Interaction — The Actually and Potentially 

 Normal — The Inevitably Abnormal — Justification of the Term Resistance 

 as Applied to Disease. 



In treating of life we have to make a distinction between 

 (a) the organism, and (b) its environment. If each of these be 

 properly constituted an inter-action takes place, and there is 

 healthy life. If S be normal and E be normal, S 4- E will 

 represent a set of material conditions which will inevitably 

 issue in healthful vital action. 



I say, if S and E be normal ; but is it possible to define a 

 normal S and a normal E ? Is there a criterion of normality 

 of S and E — a fixed standard capable of rigid definition ? The 

 answer is certainly iVb, although we are somewhat apt to 

 assume one. 



What, then, is to be understood by a normal S or a 

 normal E ? In answering this question the great fact to be 

 borne in mind is that it is quite impossible to define either 

 without reference to the other. Life being a two-sided pro- 

 cess, of which the one side is represented by S and the other 

 by E, we may say that when S + E results in healthy inter- 

 action, both are normal ; each is normal as regards the other. 

 But if S + E results in morbid action, both are abnormal ; 

 each is abnormal as regards the other. 



This position will, I believe, shortly be rendered evident, 

 and meanwhile we must ask what constitutes healthful inter- 

 action of S and E. The reply is that a condition of S and E 

 which will permit life to go on without the slightest pain, 

 and with the fullest possible enjoyment of it, until death 

 occurs through sheer wear-out, represents the ideal of health. 

 In such a case both S and E are perfectly normal. On the 



