54 THE STORY OF THE BACTERIA. 



cell communities which make up this wonder- 

 ful mechanism are all originally derived from 

 a single living cell, the ovum. 



What this mysterious thing is which we call 

 life, which from the original cell, the ovum, is 

 imparted to all the myriad specialized cells 

 which spring from it as the body grows ; what 

 it is which determines that from one of two 

 cells which under the most powerful of micro- 

 scopes look exactly alike there shall develop a 

 man, and from the other an animal, we simply 

 do not know. We theorize, we speculate, we 

 draw analogies, we give names, but at the 

 end we conclude that we must wait still for 

 more light. We do know, however, that this 

 self-built cellular mechanism, the body, which 

 is alive, has in it the power of self-renewal : 

 the power, when once started, to go on doing 

 the various things for which it is fitted for a 

 certain time, provided that the proper external 

 conditions are maintained. But sooner or 

 later the machinery begins to creak and trem- 

 ble, sometimes in one part, sometimes in 

 another, sometimes everywhere, and gradually 

 or suddenly that combination of activities 



