8 THE ORIGIN OF LIFE 



so far as to assert that luminous bodies like the flame 

 of the candle, for instance, or an incandescent mantle, 

 can be classified with living things, in their most 

 elementary states, we may say that they at least 

 partake in the process of metabolism ; and if meta- 

 bolism were the whole and the only thing that 

 constituted vital action, they would, of course, be 

 entitled to be included with such things. Flames, 

 phosphorescent bodies, and probably luminous bodies 

 generally, would thus come within the realm of 

 biology, or, more accurately speaking, constitute a 

 science in themselves such as Bio-Physics. 



We must, however, before accepting this extension 

 or this fusion of the two sciences, be careful that we 

 are not altogether over sanguine. For does meta- 

 bolism constitute the whole of vital actions, or should 

 vital processes be confined to metabolic change ? 

 This is a question which will form the subject, or the 

 subjects, of discussion in the chapters which are to 

 follow. 



The notion that all things are alive, and differ in 

 this respect only in degree, is thus fraught, it should 

 appear, with many advantages, and yet not without 

 its disadvantages. We shall see then, with all due 

 caution and reserve, which the subject naturally de- 

 mands, how far the idea permits of an extension, if 

 of an extension it admits at all. 



It is of interest to note that the notion that lumi- 

 nous bodies are in some elementary sense alive was 

 quite common to the ancients. Thus Hippocrates 

 thought that flames were living things ; whilst the 



