INTRODUCTION IS 



they may actually not occur to a significant extent 

 without its intervention. Through autocatalysis, 

 moreover, a catalyst may even produce more of 

 itself. And so in the organism we start with a 

 chemical complex of great intricacy, associated 

 with environmental conditions which are no less 

 essential than the matter in the body. It carries 

 on processes fundamentally like those of any 

 chemical system, governed by similar conditions. 

 It differs conspicuously in its maintenance of or- 

 ganized units — cells, individuals, colonies — and in 

 its ability to reproduce those units. Here lie 

 problems of life at present insurmountable, but 

 they occur like all other vital phenomena as a 

 reaction of the complex organism to the complex 

 conditions of life, and so do not destroy our concept. 

 A reasonably full discussion of the complexities 

 of living things would be a liberal education in 

 biology, but there are a few principles which indi- 

 cate a definite trend, not to say purpose, in the 

 development of organisms to their present state. 

 The primordial living substance which is a neces- 

 sary concept in our modern ideas of evolution must 

 have been very simple as compared with the sim- 

 plest cell of the present. We must assume that it 

 was a very labile protein compound; as to its 

 organization we may safely predict an absence of 

 the differentiation evident in existing cells, a closer 

 approach to homogeneity. Since life, according 



