248 General Discussion 



Wislocki: It certainly is important, in order to achieve clarity, 

 to define what one means by ageing. With respect to the 

 placenta, which I discussed yesterday, I distinguished between its 

 growth and differentiation, which represent the initial phases of 

 ageing, and of senescence which is the terminal phase. The 

 latter, furthermore, which is regressive, may be either normal 

 or pathological. I also raised the question of the difficulties of 

 ascertaining the degree of senescence which the placenta actually 

 undergoes. 



Dempsey : Is it true that growth and senescence are incompatible ; 

 that an organism is not becoming senescent while it is growing and, 

 conversely, that with the cessation of growth or the limitation of 

 growth, senescence begins? 



Bourliere: May I remind you that Prof. McCay's experiments, 

 started more than twenty years ago, have beautifully shown that 

 growth and ageing processes, although somewhat opposed, are 

 nevertheless mutually interdependent? At least, in cold-blooded 

 vertebrates it is now quite obvious that when one slows down 

 the growth rate, one increases the life-span. In other words, the 

 quicker the growth of a poikilothermous vertebrate the shorter its 

 life-span. 



Montagna: In McCay's experiments, on the other hand, many 

 factors complicate the picture; for instance, these animals are not 

 sexually mature and remain infantile. Who knows how many other 

 changes have taken place in the animal which might militate towards 

 increasing the life-span of the animal ? 



Wislocki : I would like to ask Dr. Parkes, since he can freeze the 

 hamster — as I believe he can do now for some weeks — does that add 

 to its life-span? 



Parkes : It is a shallow-freeze for only an hour or so. 



Wislocki : I see. However, do you know, if a hamster were sub- 

 jected to extensive periods of ordinary hibernation at a low tempera- 

 ture (as could be arranged experimentally) whether the time spent in 

 hibernation would be directly added to its life-span and hence 

 modify its ageing? 



Bourliere: That is exactly what happens in natural conditions in 

 the small insectivorous bats of temperate Europe and North America. 

 Such small mammals have a very poor thermoregulation even out- 

 side the hibernation period, and it has been shown that their oxygen 

 consumption is very low for about twenty hours a day, reaching 

 almost the hibernating level. Now it appears that the expectation of 

 life at birth of these small animals is far beyond that of other species 

 of mammals of similar size. Many species live more than 10 years 

 in natural conditions and it has been proved recently by banding 



