General Discussion 2i5 



tiou ol" life tcil)les iiiij>ht be an index as to what you were doing to a 

 proeess, but if you are goin<j^ to ex{)lain agein<^ as a process I think 

 ultimately you have to look at individuals, and perhaps the best way is 

 to look at them from different i)oints of view and at different levels of 

 organization. I doubt if it would be possible to formulate a definition 

 of ageing that would be acceptable to everybody and would cover all 

 the aspects of the problem as it now stands. 



Franklin: Xavier Bichat, I think, defined life as the sum of the forces 

 which resist death. Some of us find that ageing is death taking small 

 bites. 



Tunbridge: I think we shall have to accept ageing as a chronological 

 process. 



To summarize this very interesting colloquium: Dr. McCay has 

 emphasized that the conditions of experiments, however well planned, 

 may be artificial for whatever animal or insect or fish we select, and that 

 even in animal experiments disease processes must be taken into 

 account. 



Heredity was mentioned by Prof. Medawar and Dr. Comfort, It 

 obviously comes into the story, but the work seems to show that tliere 

 may be fallacies in some of the current views. We do not know to what 

 extent there is a true species difference. Differences may be due to 

 environmental conditions — as Prof. Krohn mentioned for the ovary — ■ 

 and not necessarily to chromosome determination. Throughout I think 

 we have come across the difficulty of assessing environmental factors. 

 They are difficult to control, almost impossible in man, and we tend to 

 deal with end results, instead of looking for prinxary causes; in man, 

 because of the long life cycle, we may have been too obsessed with the 

 former. We agreed that although pathological arterial changes occur, 

 they are not specific for any age group; it is a question of severity, 

 which again may be due to the passage of time. 



There was some difference of opinion among the pathologists as to 

 whether they could tell the age of a cell. Some agreed that with the 

 techniques available toda}^ it is not always possible. I think that is 

 because the methods we use fix a cell in one moment of its life cycle. We 

 can show differences in nuclear structure, but unless the protoplasmic 

 changes are gross, present day techniques do not demonstrate altera- 

 tions. It may be that there is change, but that it is not observed. 



The suggestions put forward by Dr. Parkes on the viability of tissues 

 after certain known trauma were fascinating. Why is it that when cells 

 are frozen, and maintained so for varying periods, the longer the 

 duration of freezing the greater the chance of loss of viability? At the 

 temperatures suggested it is clear that most biochemists would say that 

 the known chemical reactions have ceased to act, and therefore the 

 purely physical factors might be the important ones. 



Many speakers have emphasized the importance of sexual maturity in 

 relation to the life-span. Feeding immature animals on a low calorie diet 



