120 CICATRIZATION OF WOUNDS 



differences between healthy and cancerous tissues. In a 

 cancerous tissue the cells do not receive the order to stop, 

 or if they receive it, they are incapable of obeying. 



Thus, we are in possession of two methods enabling us to 

 study age and the process of ageing. The first in vivo, by 

 means of a complete organism, manifesting differences in the 

 rate of reparation at different periods of its evolution. The 

 second in vitro, by means of a living reagent which is eternal 

 in comparison with the short duration of our existence and 

 the activity of which is checked proportionally to the toxic 

 power developed in the serum of a normal animal by the simple 

 fact that it undergoes the limited evolutive cycle due to its rank 

 in the hierarchy of organized beings. In the first case we 

 observe the result of the accumulation of toxins and of 

 other unknown phenomena on an organism whose entire vital 

 activity is governed by the immutable cycle characterizing 

 our human condition. In the second and much simpler case, 

 we dispose of a living element, artificially removed from the 

 periodical evolution necessary to all organized beings and of 

 which only the constituent parts — the cells — eventually obey 

 the imiversal law of ageing and death. The tissue-culture 

 does not age and does not die, barring accidents. It has no 

 consciousness comparable to ours. It has no 'individual' exist- 

 ence, and only represents the summation of an infinity of 

 elementary lives. From this angle it is comparable to a species 

 rather than to an individual, for the species persists with all its 

 characteristics and without taking into account the death of its 

 members,' And yet if a culture is treated with normal serum 

 from an animal of the same species, its activity is reduced to a 

 value corresponding to the age of this animal. The flow of time 

 has therefore not had the same action on the culture as on the 

 chicken. It affects the first no more than it would an inert 

 body, whereas it inevitably sweeps the bird to its death in 

 obedience to a millennial rhythm. Not only does it affect an 

 organized being from birth, but the rate of ageing is different 



