Vlll FOREWORD 



Noiiy in the laboratories supported by the Rockefeller In- 

 stitute in France during the Great War, while he was study- 

 ing the repair of wounds. A constant relation was found to 

 exist between the velocity of wound healing and the age of 

 the patient. From the mathematical formula expressing the 

 repair of tissues, Lecomte du Noiiy extracted a constant, 

 which varies from 0.4 for a child of ten years to 0.08 for an 

 old man of sixty. In this manner, age can be detected by rate 

 of healing. The other method, much less precise, is based on 

 certain changes that take place in blood serum. During the 

 course of life, blood serum progressively acquires the power 

 of arresting the growth of tissues when they are cultivated 

 in vitro. This change is probably responsible for the decrease, 

 in function of age, in the velocity of the repair of a wound. 



The knowledge of physiological time is of obvious im- 

 portance because it leads to the understanding of its value. 

 Long ago, Minot found that the younger an animal is, the 

 more rapid is the rate of aging. From his experiments, it 

 could be inferred that physiological time has a much greater 

 velocity in youth than in old age. But we remained ignorant 

 of the extent of those differences. Their numerical value has 

 been determined by Lecomte du Noiiy. The rate of tissue 

 repair is five times slower at the age of sixty than at the age 

 of ten. 



The significance of the time of a clock depends naturally 

 on the characteristics of physiological time. When compared 

 with physiological time, physical time loses its uniform 

 value. Parents and children live in different temporal worlds. 

 They are separated by a gap that often is too large to be 

 bridged, even by illusions. Within the familial group, the 

 individuals should not be separated by too great a temporal 

 distance. It is, therefore, desirable for women to have chil- 

 dren as early in life as possible. Again, the knowledge of the 

 characteristics of physiological time teaches us that, at the 

 end of life, aging is very slow. From one year to another, 

 the appearance of an old man in good health hardly changes. 



