48 THE CAUSATION OF DISEASE. 



two come into contact, a series of associated changes ensue ? 

 which are the outcome of the " material conditions " as repre- 

 sented by the structure of germ and sperm, and the nature of 

 their environment. Each successive change in the material 

 conditions occurring during the development of the embryo 

 is the cause of those changes immediately succeeding — just 

 as the material conditions of a planetary system at any one 

 moment are the cause of the changes immediately following, 

 this new material state being again the cause of the succeeding- 

 changes, and so on to the end of time. Life, like the move- 

 ments of the planetary systems, is a simple rhythm — a per- 

 petually recurring cycle — the last changes in the cycle provoking 

 the first. This, I take it, is the explanation of all rhythms. 



The analogy I have drawn between the cycles of the 

 heavenly bodies and of living beings seems to me a just one, 

 although there is one great difference. In the case of growing* 

 organic beings matter is being continually added to the living- 

 systems, but this does not happen in the case of the planetary 

 systems. I cannot, however, afford the space to discuss this 

 matter here, and must content myself with stating my belief 

 that the two processes are, upon ultimate analysis, of a similar 

 nature, and that, given a definite structure of reproductive cells, 

 of germ and sperm, for instance, there is no difficulty in 

 accounting for the embryonic changes resulting from their union. 

 The whole difficulty, as I have said, hinges upon the cause of the 

 structure of the reproductive cells. How do these elements come 

 by their structure? Therein lies the difficulty. That germ 

 and sperm do possess a structure, and that an exceedingly 

 complex one, there can be no doubt. But here we are brought 

 face to face with the world of the infinitesimal, where our 

 senses fail us. Belying only upon these, we pronounce proto- 

 plasm to be homogeneous and structureless ; whereas reason 

 urges to a different conclusion, and in its light the tiny homo- 

 geneous flecks of protoplasm, with their infinite potentialities, 

 become two vast and complex worlds — two microcosms, in fact. 

 It were as possible for man to develop out of glass as out of 

 homogeneous jelly ! 



