THE BEGINNINGS OF LIFE. 635 



progress, however, in each case, till a condition of 

 moving equilibrium is established between the sum 

 total of molecular actions taking place within the 

 living aggregate and the forces of its environment. 



The power of undergoing spontaneous division 

 (fission or gemmation) which is manifested by living 

 matter, and upon which all the phenomena of ' repro- 

 duction ' depend, is apparently one of its most funda- 

 mental propei ties though it is itself a result of that 

 molecular mobility and complexity to which we have 

 previously referred. 



And it is this same molecular mobility which makes 

 an aggregate of living matter, in the form of a simple 

 organism, very prone to undergo changes in its inti- 

 mate constitution either c spontaneously' or under the 

 incidence of new external forces. Some new conditions 

 may not visibly affect it, others may cause its c death,' 

 whilst others still may affect it only to such an extent 

 as to bring about some modification of its molecular 

 constitution, which, by reason of an altered c polarity,' 

 entails a more or less marked transformation of form 

 and structure (Heterogenesis). 



Thus the marvellous convertibility of lower organ- 

 isms, their ability to undergo self-multiplication, and 

 their tendency to become (under favourable conditions) 

 more complexly organized, are all necessary conse- 

 quences of those physical doctrines concerning c life' 

 the truth of which has been established by such experi- 

 ments as have now been recorded. 



