82 THE BIOLOGICAL PROBLEM OF TO-DA Y 



muscle, liver, kidney, and bone tracks. Though 

 Weismann associates with germ- tracks the idea 

 that germplasm travels along them, proof of this 

 has yet to be brought forward. 



Finally, a word about the meaning of ' immortal.' 

 In a scientific work the word must be used in a 

 philosophical sense. In calling a being immortal 

 one implies both individuality and indivisibility. 

 This, at least, was the view of the old philosophers, 

 who have defined the idea of immortality. Thus 

 says Leibnitz in his Theodice: ' I hold that the 

 souls which one day become the souls of men 

 existed already in the seed, that they have existed 

 always in organised form in the ancestors, back to 

 Adam that is to say, to the beginning of things.' 



In his doctrine of immortality, Weismann has 

 not concerned himself with the two implications 

 individuality and indivisibility. He calls a uni- 

 cellular organism immortal, simply because its life 

 is preserved in the organisms arising from it by 

 division. The immortality of the unicellular forms 

 depends upon their divisibility, upon a property 

 which, according to the philosophical use of the 

 word, is incompatible with immortality. According 

 to Weismann, one immortal organism gives rise to 

 several immortal organisms, but, as these are sub- 

 ject to destruction by external agents, the separate 

 individuals are mortal. The unicellular organism 

 is not immortal in itself, but only in as much as it 

 may give rise to other organisms. In this way 

 Weismann comes in conflict with the idea of 

 individuality, and is compelled to transform his 



