l8o THE CAUSATION OF DISEASE. 



germ and sperm. This influence is more potent the earlier 

 it acts. The smallest alteration in germ- or sperm-struc- 

 ture, wrought by the subtlest force, will be sufficient to cause 

 an alteration in the development of the embryo, this altera- 

 tion increasing with every stage of development. Hence the 

 strictest care should be taken to place the mother, prior to 

 and during gestation, under the most perfect E, and we 

 should moreover be particularly careful to regulate the E 

 during the whole period of post-partem development. When 

 maturity is reached, the E is less capable of influencing S. 



Although the E possesses a considerable power in moulding 

 S, it occupies a position far below heredity in this respect. 

 This term embraces an infinite complexity of forces which tend 

 to mould the individual into the likeness of the parent or 

 parents. 



Without going any further into the question, it is sufficient to 

 say that, in the case of gamogenetic organisms, the immediate 

 cause of heredity consists in the material conditions as con- 

 stituted by the impregnated ovum and its environment. 

 Given these material conditions, the offspring will develop 

 into a more or less mean likeness of the parents. How germ 

 and sperm come by their structure is another question ; but, 

 given the proper material conditions, there is no difficulty in 

 explaining, on the principle of causation already set forth, the 

 subsequent developmental changes. 



Be it noted, that the material conditions, as constituted by 

 the impregnated ovum and its E, represent the immediate 

 cause of the hereditary process ; but in every instance of 

 causation we can increase our knowledge of the causative 

 process by tracing out the remoter links in the chain of 

 causation. Thus, if we can trace the causation of germ and 

 sperm structure — i.e., specify the material conditions out of 

 which they themselves have risen into being— we shall 

 possess a fuller knowledge of the causation of heredity. But 

 indeed, in order to get a complete and philosophical insight 

 into this marvellous moulding agency, it is necessary to cast 

 the eye into the long past, and follow, one by one, the 

 various steps of organic evolution. In this way we extend and 



