252 General Discussion 



washed a dog's stomach with eugenol, which completely denuded 

 the mucosa of the stomach, the mucosa was repaired within 24 hours. 

 This provisional repair takes place without the occurrence of mitosis. 

 The cells of the foveolae and the neck-chief cells simply expand ; they 

 glide over and very quickly repair the denuded stomach. Mitotic 

 activity comes much later, after the damage has been largely covered 

 over, and final repair of the damage takes place. 



As far as amitosis is concerned, I rather suspect that there is no 

 such thing. 



Huggett: I should not be the least bit surprised. 



Jost: I should like to return to embryonic problems. I feel that 

 ageing of a tissue involves a very important period during which 

 the potentialities of the cells are limited — what the embryologists 

 call "determination of a tissue". The time at which cells become 

 specialized for a special function is certainly a great event in a 

 tissue ; I believe that in ageing of a tissue this is an important part 

 and a first step towards senescence. 



I hope that the biochemists will define "senescence". Perhaps 

 the difference between synthetic and catabolic activities, as we were 

 told this morning for leaves, may be used. 



Williams : I do not want to take that point up but can we perhaps 

 think that senescence is a quality correlated with sexually repro- 

 duced organisms. Dr. Mollison has made the suggestion that amoeba 

 is intrinsically immortal; Dr. Yemm suggests that perhaps vegeta- 

 tively reproducing plants are immortal; the only animal tissue that 

 I can think of which, in a sense, is experimentally vegetatively 

 reproduced is the transplanted tumour which is also intrinsically 

 immortal. 



Corner: Jennings, who made a considerable point of senescence 

 not in the individual protozoan, e.g. Paramecium, but in the clone 

 (the totality of cells derived from a single mating between two 

 Paramecia), said that the offspring of a pair forms a kind of unit 

 which undergoes senescence in that its cells finally lose the power 

 to reproduce by division and the clone dies out unless one of them 

 mates again. 



I think he had a poetic notion that the clone of Paramecium is 

 like the multicellular body of a higher organism; in that sense the 

 unicellular organism was thought by him to undergo senescence. 



Williams: When it has no sexual mating. 



Corner: It sounds a little mystical because it is rather difficult 

 to see how the same fate could control the hundreds of offspring of 

 a pair so that they all lose the potency for mitotic division at the 

 same time, but this was his notion. 



Krohn : Sonneborn has been working on this recently, has he not ? 



