CHEMICAL CLOCK 163 



which is at least quahtatively in good accord with our experi- 

 ments and our reasoning. Thus only the quantitative accord 

 might be questioned, and we will take this up later. 



It may be rightly objected that not all biological phenomena 

 are slowed up by age in the same proportion as cellular 

 activity. The answer to this is that it is necessary to differen- 

 tiate between fundamental biological phenomena and the 

 others. Phenomena such as cicatrization and cellular proli- 

 feration, which are life itself, i.e. the edification of living 

 matter, must not be confused with certain physico-chemical 

 phenomena which underlie our biological activities but which, 

 as was shown at the beginning of this book, are different in 

 many ways. If, for instance, one objects that the velocity of 

 the nervous influx or irritability as a function of time — 

 measured by 'chronaxy' — is far from being modified by age 

 in the same proportion, one can answer that irritation is a 

 property of living matter which is fundamental in that it 

 determines the conditions of muscle and nerve action, but 

 which is, however, less fundamental than the manufacture 

 of the cells themselves. Irritability is an epiphenomenon. 

 Cellular proliferation is the basic phenomenon of the building 

 up of living matter. The remarkable notion of chronaxy, so 

 ably developed by the French physiologist Lapicque, should 

 be no more influenced by age than fundamental phenomena 

 such as the beating of the heart, for example. On the other 

 hand, it can be plausibly admitted that hematopoiesis — the 

 manufacture of red blood cells — is affected in the same pro- 

 portion as cicatrization. The measurement of chronaxy 

 cannot give any information concerning the age of the organ- 

 ism because it is only the measurement of a property of living 

 matter and not a measurement of the vital activity of the cells. 

 Tissue-cultures live and cicatrize their wounds without a 

 nervous system. 



A more serious objection is that the impression of the more 

 rapid flight of time is simply due to the varying ratio of the 

 length of the time unit — a year, for instance — to the total 

 duration of life. For example, a year seems longer to a child 



