2 R. E. TUNBRIDGE 



by the structure of the chromosome? We can breed animals 

 with longevity as a dominant, and it is well known that there 

 are human families in which longevity is a striking characteris- 

 tic. This is a fascinating aspect of th^ problem; Professor 

 Medawar has very strong views on this approach to ageing, 

 and we look forward to hearing his lucid exposition. 



Then again, is senescence itself a primary biological func- 

 tion? Is it inevitable or is it merely the predominance of 

 catabolism over anabolism? Is it a feature of cellular life, of 

 the life of an organ or of an organism? Alexis Carrol in his 

 experimental work suggested that environmental factors were 

 highly important, if not the most important factor in sene- 

 scence or the changes which we associate with senescence. 

 Then we have the problem of the cyclic changes that occur in 

 many organs, for example the thyroid or the ovary. Is the 

 hypertrophy and involution a fundamental biological process, 

 and is senescence allied to it, an exaggeration of it, or a 

 similar process in another phase? I understand that the 

 senescent or atrophied ovary of an adult animal can be trans- 

 planted into a young ovariectomized animal of the same 

 species, and that it then proceeds to take on cyclic function 

 again. Therefore, is it merely the milieu in which the organ 

 lives, the environmental factors, which determine age changes, 

 or are they separate and distinct processes? We have with us 

 experts like Dr. Betty Rubin, Dr. Parkes, Professor Krohn, 

 who may not deal with this particular problem, but who as a 

 result of their pre-eminence in the field of endocrinology are 

 bound to touch on similar topics. 



Then, of course, there is the extraordinary power of organs 

 or tissues to regenerate. We are familiar with the great powers 

 of regeneration of, say, the liver, and not merely the growth 

 but the readiness with which new cells take on apparently 

 normal function, whereas in other tissues, like the nervous 

 system, once the nerve cell is seriously damaged it is no longer 

 capable of repair. We have with us many experts on the 

 changes in tissues with ageing. Are the changes in the skin, 

 the arteries, the bone, the lungs, just senescence? Are they 



