98 R. E. Tunbridge 



still not known, but the purest preparations so far prepared 

 contain at least two enzymes, one of which is proteolytic. 

 Further, Hall (1955) has shown that a metal is concerned in 

 the reaction between elastin and elastase and that the metallic 

 ion is calcium. The concentration of the calcium ion is im- 

 portant and can determine the form of the reaction. Balo and 

 Banga (1949a) suggested that elastase was normally present in 

 the body but prevented from acting in the normal individual 

 due to the presence of an inhibitor. Graham and Saxl (1957) 

 have been able to confirm the presence of an inhibitor in 

 normal serum and have suggested that its action may be 

 determined by the state of the tissue with which it is in 

 contact. Thus, physical stress might provoke changes in the 

 aorta and in consequence the altered tissue might take up the 

 inhibitor substances releasing elastase and so exacerbating 

 still further the degradation. This process is also accompanied 

 by the liberation of fatty material and so other well recognized 

 features of arterial degeneration could be explained. Refer- 

 ence has already been made to the work of Lansing and his 

 finding that the amino-acid composition of elastin from the 

 aorta varies with age. We have found that the susceptibility 

 of the aorta to the action of elastase varies with age. The aorta, 

 however, is a very complicated structure. Morphologically at 

 the level of the light microscope at least two distinct forms of 

 elastic tissue can readily be observed and both are intimately 

 associated with collagen fibres. It is, in fact, extremely diffi- 

 cult to separate the collagen from the elastic material. The 

 majority of the chemical methods used to free elastic tissue of 

 collagen are drastic and undoubtedly bring about some 

 degradation of the material. It is thus very interesting that 

 elastase should show a greater degree of activity with older 

 specimens of aorta but such changes are not necessarily a 

 direct result of ageing processes but could well be brought 

 about by the effect of disease. Using elastase we have further 

 been able to show that there are chemical differences between 

 the elastic material as derived from the aorta and from the 

 ligamentum nuchae. Wood (1955), examining the extensile 



