564 THE POPULAR SCIENCE MONTHLY 



voted some years to a study of these matters in such creatures that I 

 venture to speak to you on this subject. 



You remember that one of the famous early essays of Weismann 

 was upon the question I have just raised. He tried to show that death 

 is not at all necessarily involved in living ; that natural death originally 

 did not exist, and does not exist now in these lower creatures; with 

 theology he held that death was acquired in the course of time^, and the 

 Satan that " brought death into the world and all our woe " was no 

 other than natural selection, acting for the benefit of the race, as dis- 

 tinguished from that of the individual. The body in the course of time 

 becomes worn, battered, crippled. It is well to have at intervals a 

 clearing out of this worn stock; new, fresh bodies replace the battered 

 ones and a race which nndergoes regularly this renewal must prevail 

 and perpetuate itself in the place of those that do not ; such is the con- 

 ception of Weismann. Thus, too, the snm of happiness in the world is 

 kept at the highest mark, since the fresh and perfect can enjoy much 

 more than the worn and crippled. 



But according to this view, if organisms could but live in such a 

 way as to keep the body fresh and uninjured, there would be no need 

 for death. And the organisms which have succeeded in doing this are 

 the infusoria and their relatives. These, in the famous phrase of Weis- 

 mann, are " potentially immortal." 



But another fact in the lives of these creatures attracts strongly the 

 attention of the observer. These same unicellular organisms that ap- 

 pear to live forever do likewise go through the same process of sexual 

 union that we find in higher animals. 'Now this sexual union has 

 proverbially stood as the token of mortality; it is the preparation for 

 the new generation, and prefigures the disappearance of the old one. 

 You will recall the famous remark of Alexander the Great upon this 

 point. 



Why then should this take place in these ever-living creatures ? The 

 fact that it does was held by many to indicate that to consider these 

 creatures ever-living was a mistake; they predicted that these animals 

 would be found not potentially immortal, but subject to death at the 

 end of a certain term, just as are higher animals. It is interesting to 

 discover here, as in so many other cases, that the diverse possible opin- 

 ions on the subject were formulated and maintained before investiga- 

 tion had obtained evidence as to the facts in the case. 



But men were not content to speculate; and Maupas in one of the 

 great investigations of biology (1883 to 1888) undertook to determine 

 the truth of the matter. AVe must look briefly at the questions which 

 were raised, and the answers that were obtained by Maupas and by 

 others, for it will help us to understand the present state of the matter. 



Maupas took a single individual (a Stylonychia), kept it with 

 plenty of food, and allowed it to multiply by repeated division into two ; 



