THE DESCENT OF PROTOPLASM 179 



integrating and becoming absorbed into the con- 

 stituents which composed it. This is a physical pro- 

 cess which is not merely analogous to, but essentially 

 of the same kind as, even if incomparably simpler 

 than, organic metabolism. The mechanism in each 

 case does differ in complexity, as the simplest 

 chemical or even infra-atomic actions differ from 

 the vast and complicated reactions of an incandescent 

 nebula or of the sun itself. But if we so choose 

 we might prefer to call it not organic but physical 

 life. Such peculiar types of atomic and of inter- 

 atomic systems, when acting in concert with highly 

 complicated organic compounds, can give rise to 

 further molecular actions which, partaking as they 

 do of their metabolism, and forming larger individual 

 aggregates, can assume the distinctive cellular 

 structures that, according to the circumstances 

 in which they have been formed, may be regarded 

 as types of more or less organic forms of physical 

 and even of organic life. 



Even in the production of artificial cells, like 

 those we have described, there is still the possibility 

 that even amongst the bodies thus produced there 

 may be, if the number of trials be sujfficient, 

 one or two amongst millions or billions of such 

 individuals ; one or two cells which should possess 

 the structure that would enable them to multiply 

 or reproduce to an indefinitely recurring period. 



This is the great difficulty which all experiments 

 on spontaneous generation present. Negative results, 

 however numerous, may be merely the most 



N 2 



