140 THE CAUSATION OF DISEASE. 



heredity, is a natural variation — a natural variation from the 

 structural mean. In other words, every acquisition is a natural 

 variation. The difficulty here is to distinguish, in scientific 

 language, between what is hereditary and what is acquired, 

 for it is by no means easy to say whether a structural 

 peculiarity is the distinct outcome of heredity, or whether 

 it is not rather due to the application of some specific E ; 

 but even in the latter case heredity plays a most im- 

 portant part, since it is this, as will be more particularly 

 shown later on, which determines the capacity of varying in a 

 particular way. 



Scientifically, it is perfectly justifiable to distinguish sharply 

 between the hereditary and the acquired ; practically, how- 

 ever, it is quite impossible. Scientifically, we may dis- 

 tinguish as follows : — If an individual is exposed to as 

 negative an E as is compatible with life, it is evident that 

 there will be little or no acquisition. We may, for 

 purposes of argument, assume such a negative E — an E, 

 namely, under which an individual will pass through a series 

 of developmental changes, which are the outcome of the force 

 of heredity, pure and simple — i.e., altogether independent of 

 external influences. It is, of course, impossible really to 

 exclude altogether the influence of E, since life is due to 

 the interaction of S and E. Assuming, however, such a 

 theoretic standard negative E, both ante and post partem, we 

 should then discover the individual to be that mean structural 

 product whereof we have spoken. As a matter of fact, it 

 would be utterly impossible to prevent acquisitions, for the 

 organic textures are so plastic, so impressionable, that they 

 are ever ready to be moulded by a multiplicity of diverse 

 external agencies. 



It is absolutely necessary to assume the theoretical existence 

 of a hereditary product, pure and simple, in order to dis- 

 tinguish between that which is acquired and that which is 

 inherited. Of course, we inherit the power of acquiring, but 

 we do not entirely inherit the acquisition, for if we did not 

 place ourselves under an E capable of effecting this structural 

 change or acquisition, it would never appear, and such an E may 

 in no way be necessary to life. Wherefore we are justified in 



