THE CONSERVATION OF LIFE 225 



we observe all at once a remarkable change. All the animal- 

 cules which we may take out and observe under the microscope 

 will be found to be in pairs, joined ' mouth to mouth.' It seems 

 as if the entire culture suffered from a kind of conjugation 

 mania. When this intimate union has continued for some time 

 the pairs separate and the individuals live as heretofore, swim 

 hither and thither, and divide, until after a number of genera- 

 tions they enter into a fresh union of pairs. 



What is the meaning of this mysterious process ? It is doubt- 

 less one of great importance to the destiny of the Infusorians, for 

 if it were otherwise how would it have become so universally 

 established? A light is shed upon the mystery by the classic 

 experiments made by Maupas. As conjugation usually takes 

 place simultaneously in a very large number of individuals it 

 seemed probable that its cause was to be found in the influence 

 of external conditions, an assumption which to a certain extent 

 proved accurate. It appeared that this conjugation-epidemic 

 always took place when food became scarce, but that abundance 

 of food always postponed it. It is no doubt necessary that other 

 internal conditions have to be fulfilled before conjugation can 

 take place, but we will disregard details. 



The results of preventing such conjugation are curious. At 

 first no injurious changes of any kind are perceptible and repro- 

 duction takes place undiminished : the mother-animalcules divide 

 into children, these into grandchildren, and thus generation 

 follows generation. But very soon the descendants do not seem 

 to possess any longer the same vigour as their ancestors : the 

 cilia-covering becomes incomplete : the size decreases ; all signs 

 of ' senile degeneration ' appear ; and in a short time the entire 

 colony has become extinct. If, however, the Paramcecia are 

 permitted to proceed to conjugation at the right moment all signs 

 of degeneration are absent, and the power of fission is inherited 

 undiminished from one generation to another. 



It seems, therefore, that Infusorians already die a natural 

 death, though a death which does not take place as an inexorable 

 necessity, as in the higher animals, but may be ' switched off' by 

 the mysterious process of conjugation. Maupas and other investi- 

 gators, on the basis of these observations, conceived therefore 

 conjugation to be a life-renewing process, a means of unlocking 

 15 



