THE TIME OF ORGANIZED BEINGS I47 



the same, to age, must learn anew what his parents learned 

 before him. It is the rocket which rises only to fall again. 

 The individual, therefore, evolves in a personal time which 

 has a beginning and an end. But the time of the species to 

 which he belongs, the 'wave front' time, has practically no 

 beginning and no end. As we have already stated, it is a con- 

 cept which can have no real value for any of us, any more than 

 the concept of the uniform flow of physical time. The only 

 time which counts for man is his own time, the time which 

 extends between a cradle and a tomb. 



We can attain this physiological time directly by means of 

 the two methods described in this book. The method based 

 on the cicatrization of wounds and that based on tissue- 

 cultures. We have already seen that it was possible thus to 

 obtain a measurement of the real physiological age. We shall 

 now see how a measurement of time can be derived from it. 



The reader may remember that we obtained an index of 

 cicatrization i from the rate of cicatrization of the surface 

 wounds. The following pages will show why we insisted at 

 length on the value of this coefficient, the discovery of which 

 was of greater scientific interest than the simple fact that it 

 enabled us to calculate from beginning to end the successive 

 dimensions of a wound. Thanks to it we could for the first 

 time, as was pointed out by Carrel in his admirable book, 

 Man^ the Unknown^ measure the flow of physiological time. 



Now, the value of this index (see page 79 et al.) depends 

 both on the area and on the age of the patient. It is all the 

 higher the smaller is the wound and the younger is the man. 

 It was therefore important to eliminate the part played by 

 the area and to fijid a new coefficient, independent of the 

 dimensions of the wound and truly expressing the physiological 

 activity characteristic of a given age. 



The study of a large number of experimental figures showed 

 the possibihty of obtaining such a coefficient as well as the 

 limits between which it would be appHcable. So as to enable 



