THE CAUSATION OF DISEASE. I 29 



The impossibility of any two organisms being subjected to 

 exactly the same E is evident from Herbert Spencer's dictum, 

 that "no two parts of any aggregate can be similarly con- 

 ditioned in respect of incident forces." * So that even uni- 

 cellular organisms inhabiting the same fluid medium cannot be 

 subjected to exactly the same E ; and not only this, but no two 

 parts of any one organism " are similarly circumstanced in 

 respect of incident forces." 



Hence different organisms, being subjected to forces which 

 are more or less unlike, tend themselves to become more or less 

 unlike — that is to say, they form natural variations, and not only 

 does the organism as a whole alter, but owing to different parts 

 of the same organism being subjected to different forces, the 

 structure of these different parts becomes differently modified : 

 the homogeneous passes into the heterogeneous. Now if the 

 E can never be the same even for simple organisms, we see 

 how utterly impossible it is that it should be the same for such 

 a complex organism as man. 



The Influence of the Ante-partem E upon S. — Let us, 

 for instance, consider briefly man's ante-partem E. In so 

 doing, it will be necessary, of course, to start at a period ante- 

 cedent to the birth of germ and sperm, and to inquire into the 

 conditions under which they come into being ; and it will be 

 further necessary to take account of the agencies environing the 

 embryo to which they give origin. Concerning the former, it 

 is manifest that the circumstances under which germ and 

 sperm spring into being, and the subsequent E of each, must 

 differ from time to time with the general bodily health of the 

 father and mother, with the kind of food taken, the amount of 

 physical exercise, and so forth. We can well understand how 

 these and other conditions, many quite outside our knowledge, 

 may so modify the cell-E of the tissues, including those of 

 ovary and testicle, as to lead to differences in their cell struc- 

 ture — to deviations, that is, from the ideal form — and, conse- 

 quently, to differences in the reproductive elements to which 

 these latter structures give origin. Even supposing, however, 

 the bodily state of the parents to be exactly the same from day 



* See Spencer's " First Principles," § 109. Also Spencer's " Biology," 

 vol. i. § 88. 



