THE GENERAL CONDITIONS OP LIFE 343 



leaves untouched the phenomena themselves, for in the end it is a 

 matter of taste, whether the appearance of a corpse, or, what is 

 more general, the end of the individual existence, is regarded as 

 the essential factor of death. 



The fundamental distinction which Weismann makes between 

 unicellular and multicellular organisms respecting immortality 

 may be attacked from another side. As has been seen, Weismann's 

 theory of the immortality of unicellular organisms rests upon the 

 supposition that the reproduction of these forms by division can 

 go on without end, without any remnant, any corpse, being left over. 

 It is a question whether this supposition is correct. 



A few years ago Maupas ('88) carried out upon Infusoria a 

 series of striking researches, from which it appears that in that 

 group this is not the case. He bred Infusoria in cultures for 

 many generations, and found that after a large number of succes- 

 sive divisions the individuals gradually showed changes that led 

 inevitably to death, unless after a long period of dividing, leading 

 often to hundreds of generations, the opportunity was given them 

 to conjugate, i.e., to enter into a correlation that corresponds in 

 unicellular organisms to the process of fertilisation in higher 

 animals.^ Only when a series of divisions was followed by a 

 period of conjugation were the individuals separating after conju- 

 gation in condition to divide again unchanged without passing 

 gradually into death. If, however, the individuals were isolated 

 after every division, after some time they inevitably died. There 

 is here presented, therefore, a real phenomenon of old age, which 

 corresponds completely to the senile atrophy of tissue-cells in 

 man and the higher animals, and Maupas himself was forced to 

 reject Weismann's doctrine of immortality. But at this point, to 

 save the doctrine, Gruber ('89) speaks a word for Weismann and 

 says : " It is true that those individuals that by chance do not 

 conjugate, perish, but the material of the others lives on for ever." 

 Since now, in nature conjugation is the custom — for, otherwise, 

 the Infusoria would long since have become extinct — the members 

 of this group, Gruber thinks, are really immortal. Although the 

 justice of this argument is to be recognised, another fact should 

 be noticed. R. Hertwig ('88-'89), who studied very carefully the 

 events of conjugation, found that a part of every cell dies during 

 the process, viz., the macro-nucleus and a part of the daughter- 

 nuclei, derived by continuous division of the micro-nuclei. These 

 constituents of the cell break up into small fragments, which 

 finally become completely dissolved in the protoplasm.^ In other 

 words, portions of the individual actually die. That the material 

 derived from their disintegration is finally consumed again by the 

 cell, like the ingested food, does not banish the fact that these 

 parts really die. The cells that disintegrate in the histolysis of a 

 1 Cf. p. 200. ' Of. p. 201. 



