Discussion 69 



certainly get postmortem material and I should have thought that the 

 ligamentum nuchae in the ox could be obtained. 



Tunbridge: There is a very simple evidence — it is not complete — in 

 the human. If you take the tendo Achillis of a foetus or of an infant up 

 to about five or six months, there are marked differences in structure at 

 whatever light level you employ, i.e. the light or electron microscope; 

 the tendon gradually assumes an ordered form with increasing age. 

 One has to be careful about the interpretations of things seen at different 

 light levels, but the physical chemist would accept that the form of the 

 tendon in the foetus is different from that obtained from an infant over 

 the age of six months. It has been suggested that the change arises as a 

 result of walking, but we have found it to be present before six months 

 whether the child walks or not. The tendon seems to retain the morpho- 

 logical appearances obtained at six months throughout the rest of life. 

 Changes do occur but one cannot exclude the possibility that such changes 

 are the result of trauma or disease. One must be very careful of saying 

 that changes, because they are associated with chronological age, are 

 automatically the result of an ageing process. There is evidence for 

 structural changes in young tissue which may have biological signifi- 

 cance, but one must not infer that they occur because of ageing. 



Verzdr: The 5-month-old rat is young, the 10 to 18-month-old one is 

 in the prime of life, from 18 to 24-months old I would call it an old rat and 

 after 24 months it is a senile rat. The rough morphological picture of the 

 tendon fibre is not changed in the rat from the fifth to the twenty-fourth 

 month, and during this time there is continuous change of the force of 

 thermic contraction. 



Landowne: We have made some observations on humans which may be 

 relevant here. We used an external stimulus to set up a pressure-wave 

 in a living human brachioradial artery. This has only the advantage 

 that the subject is living at the time, but it has the great disadvantage 

 that we have no dimensional data, so the following is not a physical, 

 but a physiological, study. We were able to relate the pressure existing 

 at the moment to the velocity of propagation of such a pulse-wave 

 (1951, Fed. Proc, 10, 78; 1952, J. GeronL, 7, 485). I shall ask you to 

 accept the square of the wave velocity as an approximate index of the 

 change in distensibility of the vessel, as pressure changes. With age, the 

 relation between velocity and pressure changes: in the young individual 

 we have a curve concave to the pressure axis ; in the older individual the 

 curve tends to be initially higher, but to rise more slowly and to show less 

 curvature. While absolute level changes with age at some pressure levels, 

 it does not change in our material at other pressure levels. This is a 

 study of age clinically, i.e. the agewise differences include all the things 

 that man is heir to, and specifically this includes Monckeberg's sclerosis. 

 But in speculating upon the possibilities behind this, it appeared that 

 the change in distensibility with a change in stress was less in the old 

 individual and we felt this could be accounted for by an increase in 

 cross-linking or change in the mobility of the long-chain molecules. 

 Here, of course, we are dealing with a very complex structure that has 

 much more than collagen in it. 



