40 THE INFLUENCE OF INANIMATE SUllBODNUINGS. 



SECTION II 

 THE INFLUENCE OF INANIMATE SURMOUNDINGS. 



CHAPTER II. 



FOOD AND ITS INFLUES[CE. 



The necessity of nourishment. — It is universally known that 

 most animals begin their existence as very minute, often indeed 

 microscopic, elementary bodies, as eggs which are simply cells 

 and usually immeasurably smaller than the parent animal. 

 This disparity of size is most marked among the mammalia, the 

 most highly developed group of the animal kingdom ; the ovum 

 cell being always microscopically small, while the animals are 

 often of gigantic size. This difference of size shows, without 

 any further proof, that in most cases the nutriment present in 

 the ovum must receive further additions of organic matter ^ to 

 enable the animal to acquire its proper size ; and as animals 

 cannot, like plants, form these matters themselves by the decom- 

 position of carbonic acid, they must take it up from external 

 sources in the form of ready elaborated organic tissues^ — which 

 is equivalent to saying that animals must derive the organic 

 portion of their nutriment from other oi-ganisms. The need of 

 the growing animal for such organic nourishment is, as we well 

 know, very great. 



But this imperative need of constantly adding new supplies 

 of organic matter during the period of growth to the nutriment 

 which the young animal has derived from the egg is not the 

 only cause which obliges it to be always seeking nourishment ; 



