I.] APPENDIX. 6 1 



says, referring to animal life ^ : ' L'observation des faits y attache 

 I'idee d'une terminaison fatale, bien que la raison ne decouvre 

 nullement les motifs de cette necessite. Chez les etres qui font 

 partie du regne animal rexercice meme de la renovation mole- 

 culaire finit par user le principe qui I'entretient sans doute 

 parceque le travail d'echange ne s'accomplissant pas avec une 

 perfection mathematique, il s'etablit dans la figure, comme 

 dans la substance de I'etre vivant, une deviation insensible, et 

 que I'accumulation des ecarts finit par amener un type chi- 

 mique ou morphologique incompatible avec la persistance de 

 ce travail.' 



Here the replacement of the used-up elements of tissue by 

 new ones is not taken into account, but an attempt is made to 

 show that the functions of the whole organism necessarily cause 

 it to waste away. But the question at once arises, whether 

 such a result does not depend upon the fact that the single 

 histological elements, — the cells, — are worn out by the exercise 

 of function. Bertin admits this to be the case, and this idea of 

 the importance of changes in the cells themselves is everywhere 

 gaining ground. But although we must admit that the histo- 

 logical elements do, as a matter of fact, wear out, in multicellular 

 animals, this would not prove that, nor explain why, such 

 changes must follow from the nature of the cell and the vital 

 processes which take place within it. Such an admission would 

 merely suggest the question : — how is it that the cells in the 

 tissues of higher animals are worn out by their function, while 

 cells which exist in the form of free and independent organisms 

 possess the power of living for ever ? Why should not the cells 

 of an}^ tissue, of which the equilibrium is momentarily disturbed 

 by metabolism, be again restored, so that the same cells con- 

 tinue to perform their functions for ever : — why cannot they 

 live without their properties suffering alteration .? I have not 

 sufficiently touched upon this point in the text, and as it is 

 obviously important it demands further consideration. 



In the first place, I think we may conclude with certainty 

 from the unending duration of unicellular organisms, that such 

 wearing out of tissue cells is a secondary adaptation, that 

 the death of the cell, like general death, has arisen with the 



' Cf. the article ' Mort ' in the ' Encyclop. Scienc. Med.' vol. M. p, 520. 



