156 TIME 



Now, when a wound cicatrizes, what does it do? It effectu- 

 ates a piece of work. Just as a mason closes up a breach in a 

 wall, nature repairs a breach in our organism. When we 

 measure the velocity at which this work is accomphshed, by 

 means of the sideral, physical time, we observe that it is very 

 great at the beginning of life, slower at the middle and slower 

 still towards the end of life. We can see on Fig. 28 that if 100 

 represents the velocity at twenty years of age, at thirty it is 

 only 76 and at sixty 31. But it is expressed by 155 at ten 

 years of age. It is therefore not constant with respect to our 

 unit of measurement, the 24-hour day. At different ages it 

 takes different lengths of time to accomplish THE SAME AMOUNT 

 OF work: the cicatrization of one square centimetre of a wound. 



On the other hand, it is possible to evaluate time by referring 

 to a travelled distance or to a work done, if one is reasonably 

 sure that the speed of displacement has been constant in the 

 interval or if the workman has not changed the rhythm of his 

 movements. We often employ expressions such as: the time 

 to go to the post office, the time to dress, the time to write a 

 page. In olden days, the hours of a trained labourer, working 

 regularly, were often estimated by the work accomplished, for 

 instance by the area mowed. Supposing he cuts, on an 

 average, two hundred and fifty square yards an hour. If he 

 has worked four hours we know that he has cut a thousand 

 square 3'ards. But if we have no watch and do not know how 

 long he has worked, the measurement of the mowed area, two 

 thousand square yards, for example, enables us to conclude 

 that he has worked eight hours. We have therefore measured 

 time by the amount of work performed. Consequently, if we 

 reason in the same way for the work represented by the 

 cicatrization of a wound, we can measure sideral time in units 

 of physiological time. 



An objection immediately imposes itself. We have just 

 demonstrated that this work is accomplished at different 

 velocities at different moments of our life. We are therefore 

 no longer under the required condition. Not only is it im- 

 possible for us to affirm that the work has been accomplished 



