60 THE DURATION OF LIFE. 



tissues in consequence of their functional activity. Bertin says, 

 referring to animal life * : ' L'observation des faits y attache 1'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 1'exercise meme de la renovation moleculaire Unit 

 par user le principe qui 1'entretient sans doute parceque le tjra- 

 vail d'echange ne s'accomplissant pas avec une perfection ma the - 

 matique, il s'etablit dans la figure, comme dans la substance de 

 1'etre vivant, une deviation insensible, et que 1'accumulation des 

 ecarts finit par amener un type chimique ou morphologique in- 

 compatible 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 histological 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 ? AVhy 

 should not the cells of any tissue, of which the equilibrium is 

 momentarily disturbed by metabolism, be again restored, so that the 

 same cells continue 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 complex, higher organisms. 

 Waste does not depend upon the intrinsic nature of the cells, as the 

 1 Cf. the article ' Mort' in the ' EDcyclop. Scienc. MSd.' vol. M. p. 520. 



