66 F. Verzar 



to inhibit the thermal contraction of the fibre. We have 

 reached the conclusion that the explanation of this phenome- 

 non must be an increase in "cross-linkages", perhaps of 

 hydrogen bonds, between the collagen molecules of the tendon 

 fibres in the aged (Verzar, 19556 and c, 1956). The same 

 mechanical changes of thermal contraction as in the isolated 

 collagen fibre can be seen in whole skin and also in the whole 

 nerve (Verzar, 19556). 



It is possible that a mechanism of ageing of filamentous 

 proteins, such as collagen, has thus an even more general 

 interest. Many biologically important proteins are filamentous 

 molecules, like insulin and the nucleotides of the chromosomes, 

 etc. If ageing means an increase in "cross-linkages", then 

 this process might occur also in other proteins in a manner 

 similar to that seen in the tendon of the rat's tail. 



If it were realized that an increase in cross-linking is a main 

 process of ageing in molecular dimensions, then it might even 

 be possible to approach experimentally the question of its 

 decrease. Curiously enough, the tanning industry may 

 already have the greatest experience, one which we can use in 

 future studies on ageing (Bjorksten, 1951; Wood, 1954). A 

 destruction of cross-linkages in general may be able to post- 

 pone ageing, especially in certain tissues, perhaps in the 

 collagen-containing tissues of joints and tendons. 



Parallel to these changes in the collagen fibre, there are others 

 which break it down to elastin-like tissue (Banga, 1953; Hall, 

 Reed and Tunbridge, 1952, 1955a and b, 1956). These changes 

 are in many ways similar to those which can be shown ex- 

 perimentally by thermal and some chemical influences on the 

 collagen fibre. The thermal contraction starts with a break- 

 down of mucopolysaccharide from the filamentous protein of 

 the collagen fibre ; if the temperature is high enough, this leads 

 to a contraction. This process can be much accelerated, or the 

 temperature at which contraction occurs can be much lowered, 

 by acids. I only want to point out, in a rather hypothetical 

 way, that we are approaching here the problems of the causes 

 of elastosis of the human skin. 



