Discussion 71 



of known ages found in individuals of different ages, i.e. does a young indi- 

 vidual lay down collagen of a kind different from the collagen which an old 

 individual lays down under similar experimental conditions ? And, in indi- 

 viduals of different ages, does the scar tissue itself age in different ways ? 



Welford: I should like to comment on the part of Prof. Verzar's talk 

 dealing with change of adaptability with age; and to link this to the 

 discussion of variability with which we began this morning. We, in our 

 studies of behaviour, have found this increase in variability as one goes 

 up the age scale, but the precise form of its change with age has led us to 

 suspect that in a number of cases one is observing a pattern of events 

 somewhat as follows: among the younger age groups potential capacity 

 exceeds the demands of the task; in other words, some factor other than 

 the capacity that one is studying is holding performance constant. 

 The potential capacity is gradually changing, however, with age, and 

 eventually falls to a point at which it becomes the limiting factor. As a 

 result, we have a system in which up to a point one has a limitation 

 imposed by some factor which does not change with age, but beyond 

 this point there is functional dependence upon a capacity which does 

 change. Now, this has two important implications; the first is that if 

 you test performance with a task which stretches even a young person's 

 capacity to the maximum you will get a fall off at an earlier age than if an 

 easier task is used. Secondly, it has an important bearing upon the type 

 and cause of variability that one would expect to find. One normally 

 thinks of increased variability among older people as the result of people 

 ageing at different rates, but this is not the only possible cause. If what 

 I have been saying is true, one would expect to find some factor such as 

 the demands of "reasonable" performance determining the level of 

 performance among the younger subjects, but that as one went up the 

 age scale so the performances of more and more people would be limited 

 by failing capacity. For those of higher initial capacity, however, such 

 limitation would not begin until a relatively late age. Thus, during 

 middle and early old age one might expect a gradually diminishing num- 

 ber of people to maintain a performance comparable with that of young 

 people while others showed more and more profound changes. The 

 increasing variation, however, would not be due to different rates of 

 ageing but to differences of initial capacity existing throughout life, but 

 masked until middle or old age. 



Tunbridge: I should like to go back to Prof. Franklin's work on the 

 effect of using a toothbrush. This is a fascinating study not necessarily 

 confined to the problem of ageing. Does he not think that in the human 

 there may be marked differences in the method of brushing unless it is 

 supervised ? 



There is some evidence that there is a greater tendency for keratiniza- 

 tion to take place more readily in mature than in young tissue. Does 

 Prof. Franklin wish to suggest that there is a greater degree of change 

 with increasing age or is he merely re-emphasizing the differences 

 between young and mature tissue? 



Franklin: We realize that it is difficult to get patients to brush in a 

 completely standard fashion, but we are taking preliminary steps to 



