18 CREATIVE EVOLUTION [chap. 



theory according to which the diminution bears on the 

 quantity of nutritive substance contained in that "inner 

 environment" in which the organism is being renewed, 

 and the increase on the quantity of unexcreted residual 

 substances which, accumulating in the body, finally " crust 

 it over." 1 Must we however — with an eminent bacteri- 

 ologist — 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 develop- 

 ment 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 con- 

 tinuum. 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 case, 



1 Le Dantec, L'Individualiti et I'erreur individualiste, Paris, 1905, 

 pp. 84 ff. 



2 Metchnikoff, La D&j&nerescence s&nile (Annee biohgique, iii., 1897, 

 pp. 249 ff.). Gf. by the same author, La Nature humaine, Paris, 1903, 

 pp. 312 ff. 



