General Discussion '27 



great diniculty. ThcMi we'd have to resort to statist ieal analysis, taking 

 say 1,000 people of different ages, levelling it off by eliminating indivi- 

 dual variations. There might not be as great individual variations as we 

 think in this turnover. 



Brull: The main outlooks which have been pronounced here this 

 afternoon about ageing are (1) compensation and (2) adaptability. We 

 know^ that we can lose a great deal of our main tissues and still com- 

 pensate with what is left of them. We stress too much the lesions we 

 liave, and forget that if what is left of normal (or what we consider as 

 normal) tissue is able to adapt itself to the situation, then we do not die. 

 May I ask some of those here to consider how normal tissue changes 

 even without arteriosclerosis or tmiiour, how it loses its elasticity and so 

 on. And why is it no longer able to adapt itself, is that not ageing? Of 

 course, when too much of a tissue is lost, then we can no longer adapt, 

 but when .50 per cent is lost, then we may have more than enough to 

 adapt. We can produce collateral circulation, hypertrophy, dilatation 

 of the heart and so on to adapt the organism. It is the magnitude of this 

 possibihty of compensation and adaptation of the normal tissue which 

 is left which gives the measure of further life-span. 



Cowdry: You could put it in a word, couldn't you, by saying that it is 

 the ability to maintain steady states in the tissue groups — homeostasis. 



Lansing: It seems to me that Prof. Medawar was trying to be very 

 diplomatic in his presentation, and trying to keep everybody happy. 

 He had both sides of the picture: the built-in, or the endogenous ageing, 

 and the recurrent stresses, the pathological and exogenous factors. Can 

 we accept the point of view^ that recurrent stresses operate to bring 

 about dow^nfall of the organism? Do w rinkles really come from repeated 

 wTinkling of the brows, smiling and frowning, or do they come when the 

 smiles and the frowns are imposed on an ageing substrate? I have in 

 mind Dr. McCay's work with rats almost twenty years ago. Dr. McCay, 

 you kept a group of rats, didn't you, apparently far beyond their normal 

 life-spans, by inhibiting normal maturation, keeping the animals on a 

 limited diet? These rats, as I recall their photographs, were remarkably 

 young-looking at one thousand days of age or thereabouts; they didn't 

 show the w Tinkling or the patchy fur and so on although I presume that 

 the recurrent stresses were still operating. I think that this work is the 

 key experiment that's been done in gerontology so far. The w^hole hub 

 of the ageing problem is there. If one keeps an animal from maturing, 

 it doesn't age. The concept that ageing begins at fertilization doesn't 

 hold up. There were some pathological changes in those rats, but I 

 don't remember the details. 



McCay: Not till they were very old. It seems that in an anmial where 

 the epiphyses do not seal, as in the rat, there may be some key to ageing 

 in the bones. We are still studying that phenomenon. It defeats not 

 only the pathology apparently but also defeats the genetic tendencies, 

 because in our colony a few females contribute in any experiment most 

 of the very long-lived rats and a few other females contribute the very 

 short-lived rats. So it seems there is a genetic factor that is inherited, 

 there are tendencies towards certain tyT)es of disease, but when the rat is 



