t INDIVIDUALITY AND AGE 19 



bears on the quantity of nutritive substance contained 

 in that &quot; inner environment &quot; in which the organism is 

 being renewed, and the increase in the quantity of un- 

 excreted residual substances which, accumulating in the 

 body, finally &quot;crust it over.&quot; 1 Must we, however with 

 an eminent bacteriologist declare any explanation of 

 growing old insufficient that does not take account of 

 phagocytosis ? 2 We do not feel qualified to settle the 

 question. But the fact that the two theories agree in 

 affirming the constant accumulation or loss of a certain 

 kind of matter, even though they have little in common 

 as to what is gained and lost, shows pretty well that 

 the frame of the explanation has been furnished a -priori. 

 We shall see this more and more as we proceed with 

 our study : it is not easy, in thinking of time, to escape 

 the image of the hour-glass. 



The cause of growing old must lie deeper. We 

 hold that there is unbroken continuity between the 

 evolution of the embryo and that of the complete 

 organism. The impetus which causes a living being 

 to grow larger, to develop and to age, is the same 

 that has caused it to pass through the phases of 

 the embryonic life. The development of the embryo 

 is a perpetual change of form. Any one who attempts 

 to note all its successive aspects becomes lost in an 

 infinity, as is inevitable in dealing with a continuum. 

 Life does but prolong this prenatal evolution. The 

 proof of this is that it is often impossible for us to say 

 whether we are dealing with an organism growing old 

 or with an embryo continuing to evolve ; such is the 



1 Le Dantec, L Individuality et Verreur individualiste, Paris, 1905, 

 pp. 84 . 



2 Metchnikoff, &quot;La Deg&nerescence senile&quot; (Annte biologique, iii., 1897, 

 pp. 249 ff.). Cf. by the same author, La Nature humaine, Paris, 3903, 

 pp. 312 ff. 



