24 General Discussion 



that this was a dangerous generahzation. Surely regular usage is one of 

 the features of our physical training and attainment of efficiency? 



Verzdr: One of the main difficulties in all research on old age lies in the 

 fact which Prof. Medawar mentioned: the great difference in survival in 

 an otherwise equal colony. Speaking of work on rats, I know that my 

 rat colony is dying away in a similar curve to that which Prof. Medawar 

 has just described. What we would like to know is whether a certain 

 individual belongs to the group which will die under the 50 per cent 

 probability of twenty-four months, or whether it might belong to those 

 which survive to even forty-one months, as sometimes happens in our 

 colony. A measurement of certain activities could lead to an under- 

 standing. One way we tried was by studying the adaptation capacity of 

 an individual to low atmospheric pressure. It turned out that there are 

 some rats which adapt very well, while others, even at the age of twelve 

 or fourteen months, do not. It might be possible that with such an 

 activity measurement we can differentiate between those individuals 

 wliich are biologically old and others which are biologically still young 

 I should like to ask whether Prof. Medawar thinks that such a method, 

 would lead to a measurement of individual biological age? 



Medawar: I think adaptability is an admirable measure of "vitality". 

 In Prof. Verzar's example one is presumably measuring cellular replace- 

 ment, hsematopoiesis, the power of the number of red cells to rise and 

 so to adapt the animal to the low pressure. It sounds a simple and 

 neat method of measuring what is obviously a profoundly important 

 biological function. 



Cowdry: I am very much interested in both Prof. Medawar's and Prof. 

 Cameron's presentations, and I think they afford an admirable back- 

 gTound for any discussion on just what ageing is. It's my impression 

 that we all agree that every tissue and almost every cell ages differently 

 from the next one, that we are really a medley of different replacements 

 and different ages, that there are man^^ histological tests for ageing as 

 well as functional ones, that the test of performance is really as good as, 

 or better than, the test of vulnerability. I am impressed, of course, with 

 the statements of Prof. Cameron about cancer and arteriosclerosis and 

 the pattern that is presented in these numerous autopsies here in 

 London. What strikes me is the probability that the pattern would be 

 altogether different in some other countries. I know that the cancer 

 pattern shows geographical differences; for instance, intra-oral cancers 

 in Bombay are very nmnerous indeed, and in Japan gastric cancers 

 exceed all the other death-dealing cancers. Arteriosclerosis is rather 

 conspicuous in England and in the United States, and is very much less 

 so in certain Oriental races, and these two major variables change the 

 whole picture or spectrum of age changes, it seems to me. When we 

 were discussing the organization of our book on problems of ageing, the 

 first question that we were asked to come to some agreement about was: 

 what is to be regarded as normal and what as pathological? We couldn't 

 reach any conclusion, but I think that we would have liked to use the 

 statistical definition of normality if we had the necessary information. 

 That is, that the normal is the usual in a similar population, whether it 



