THE CAUSATION OF DISEASE. 299 



construct such a proximate standard, and it is more or less 

 necessary to do so, but let it be borne in mind that it can be 

 no more than a ''proximate'*' standard. The simplest way to 

 erect one will be by constructing a theoretical standard E ; 

 having done this, our task is completed, for a normal S may 

 then be defined as one which interacts healthily with such a 

 standard E. We might, indeed, attempt the definition of a 

 normal S first ; the standard E would then be one which would 

 allow such a normal S to live healthily in it. But it is far 

 easier to begin with the E, for, complex though it is, it is 

 infinitely simpler than 8. 



We have seen that individuals differ enormously in their 

 response to different modes of E. Now we can, in theory, so 

 narrow the E as to exclude all that which is capable of 

 working ill on any individuals, and to include only that 

 which shall have a beneficial action on all. In order to do 

 this we must contract it to the narrowest limits, including 

 in it, indeed, only the positive essentials to life, such as food, 

 warmth, air, and so forth, and excluding every non-essential. 

 But, even with such restrictions, how are we to fix upon the 

 standard diet, temperature, and atmospheric conditions ? 

 Different races, and, moreover, different individuals, differ 

 much in respect of the kind of food best suited to them, and 

 a like difference obtains in regard to climate. Wherefore 

 this, our standard E, can be proximate only, and further, it 

 is theoretic only : it would be quite impossible to obtain such 

 an E. 



Then as to S : as I have said, we may regard it as at least 

 potentially normal if there exists anywhere an E in which 

 healthful inter-action with it can take place. Thus, according 

 to Salter, there is probably no case of true asthma but might 

 be cured by residence in some particular part of the earth ; 

 hence, such a place must be regarded as normal to the asth- 

 matically-inclined S, and the latter normal as regards it. It 

 may be thought that it is absurd to regard an individual 

 prone to asthma as structurally normal ; but, if we push the 

 matter to its logical conclusion, there is no escaping this 

 result. 



Nevertheless, for ordinary purposes, the be&t test of nor- 



