Adaptation and Study of Ageing 65 



It is, however, astonishing how these experimental psycho- 

 logical studies have revealed enormous individual differences 

 in psychical ability in old animals of equal age, from a memory 

 comparable to that of a youth up to complete senility with loss 

 of memory. 



The loss of memory seems to show a basic parallelism to our 

 findings on retained physiological adaptation to low pressure. 

 The old individual loses the capacity to readapt himself to a 

 situation which he experienced some time ago, and to which 

 at that time he had become adapted. If this parallelism is 

 accepted, we may rightly ask whether one should search here 

 for a basic cellular process — perhaps in the central nervous 

 system only — which in young animals leads to "retained" 

 reactions or to "remembrance", and which is damaged or is 

 lacking in the old. 



Such were our thoughts when we turned to the study of the 

 physical adaptation capacity of connective tissue. Adapta- 

 tion to mechanical stress needs an adaptability of collagen and 

 of elastic fibres. Much has been said about the decrease in 

 elasticity with age. In the arteries, this leads to decreased 

 adaptation to the changes in blood pressure. The mechanisms 

 of these changes have been explained as an effect of a diminu- 

 tion of elastic fibres and an increase in elastase activity, 

 either directly or by a change in the concentration of an 

 antagonist. Thus, changes in enzyme activity have been 

 suspected as a cause (Banga, 1953). 



A remarkable change in our attitude is in progress at 

 present owing to the fact that it is understood that collagen 

 can change into an elastin-like substance (Hall, Reed and 

 Tunbridge, 1952, 1955a and b, 1956). I only wish to mention 

 this much-discussed territory in order to show that the ageing 

 of collagen has become of great general interest. We studied 

 it with the hope of finding such basic changes as might help 

 us to understand the decreased adaptability for mechanical 

 purposes in the aged. We chose a collagen tendon fibre, and 

 we found that with increasing age an interesting phenomenon 

 starts. The older the animal, the larger the loads necessary 



AGEING — III — 3 



