164 TIME 



of five than to a man of fifty because it represents the fifth of 

 his existence, whereas it represents only the fiftieth part of the 

 Hfe of the older man. This would imply a notion of time based 

 on memory, and a permanent subconscious confrontation of 

 the time which flows with the time elapsed since birth. This 

 objection is important because it is full of common sense. 

 Let us examine it with the attention it deserves. 



First of all, what can be the mechanism of this memory? 

 We are not speaking of the memory of precise facts standing 

 out against the moving background of our existence, but of the 

 registration of the very motion of this mobile background. It 

 is somewhat as if we were in a theatre watching the play of 

 actors — representing our internal perceptions projected out- 

 side of us — and as if the scenery were being shifted always in 

 the same direction, unwinding itself on the right and being 

 rolled up on the left. From a mechanical point of view it is 

 easy to conceive that the more canvas is wound the larger 

 will be the diameter of the roll and the greater will be the 

 velocity. But this is much too crude a comparison. Can we 

 find among known biological facts a basis which would allow 

 us to visualize this quantitative recording of past time? 

 Indeed we can, for we know that ageing introduces chemical 

 modifications into our organism, the effect of which is pro- 

 gressively to increase the toxicity of our serum, that mirror of 

 our physiological reactions. This fact stands out clearly in 

 the experiments of Carrel and Ebeling, described in detail on 

 p. 116. There is, consequently, an accumulation of toxic 

 products in the fluids of our organism. We know, on the other 

 hand, that the activity of physiological reparation evolves 

 parallel to this phenomenon and that the curves representing 

 the growth-index of tissue-cultures and the index of cicatriza- 

 tion assume very nearly the same aspect. The two pheno- 

 mena can almost be superposed. It may be inferred that they 

 are basically very similar. The older the individual from 

 which a serum proceeds, the more toxic his serum becomes 

 for tissue-cultures and the slower will the individual cicatrize. 

 Here is a biological fact which indicates that each year in 



