244 General Discussion 



Shock: X tliink the nrjiunicnt that because two different ijhenomena 

 can be made to fit the sainc jnatheniaticjd fornuilation they liave 

 common j)rocesscs behind them is an extremely hazardous one. 



Lansinii: I said only that it's a possibility, I'm not prepared to say 

 that we have as many kinds of proto})lasm as we have species. I think 

 there is a common proto})lasm with basic properties of multiplication 

 and o'rowth, decline, irritability and so on, varying in detail, not in 

 principle. 



Comfort: Does that imply that j^ou think that senescence is probably 

 inherent in all metazoa? 



Lansing: In so far as we can observe it, it is a natural phenomenon. 

 I would Hke to avoid the implication that because it may be inherent 

 it must be inevitable. 



Comfort: I was wondering about the case of the sea anemone. At 

 Edinburgh there Mere sea anemones which were in captivity for about 

 ninety years without any change in shape; they apparently grew new 

 cells at one end and knocked off cells at the other end, and they continued 

 to form like a cloud over a mountain. They appear to be an example of 

 indeterminate groM-th combined with definite size. And I see Brien in 

 a recent article (Biol. Rev., 1958, 28, 808) has been claiming the same 

 thing for Hydra. 



Lansing: But for instance the protozoa were held to be contradictory 

 to this hypothesis until the work was done, and then we found that 

 there is senescence in protozoa just as there is in any other species, 

 imless a particular biological process intervenes, autogamy or conjuga- 

 tion. In the absence of the latter, Paramecia go on to die, following 

 survival curves very much like those for man. 



Shock: I would agree that protoplasm is probably fundamentally 

 much the same stuff, although we know that various tissues develop 

 different functions, so that their enzyme systeins must vary quite 

 widely between different cells in the same animal. To that extent, I 

 would agree that perhaps if you knew what it was that caused a cell to 

 lose its ability to maintain concentration gradients, maintain its 

 metabolic processes, you would be a long way toward understanding the 

 ageing process. But it seems to me that the techniques that we have for 

 inv^estigating single cells are very meagre. Dr. Cowdry feels that if you 

 take a cell out of its tissue it is no longer a cell. If we accept this position 

 we are limited to unicellular organisms for study, but unfortunately 

 most of these species simply divide and form two new cells so that 

 "ageing" fails to occur. Thus, we are faced with the problem of studying 

 more complex animals or tissue, using both biochemical and physio- 

 logical techniques. Since changes in the environment of the cell, pro- 

 duced by changing the diet of the animal, will often result in alterations 

 in cellular enzymes, it seems to me that perhaps we are going to have to 

 look at the problem of ageing from a number of different levels simul- 

 taneously and not try at the moment to conceptualize the entire 

 f)roblem in one framework. Prof. Medawar has approached the problem 

 from a statistical evaluation of life tables; I am not prepared to accept 

 this a{)proach as the only way out of the dilficulties. I think the examina- 



