xi THE ALBUMINOIDS 555 



to these albumoids. The numerous substances described by Kruken- 

 berg, and called onuphin, spirographin, neossin, etc., are not dealt 

 with. It is very doubtful as to whether these substances are separate 

 individuals, and Krukenberg's descriptions are so contradictory and so- 

 much permeated by theoretical speculations that it is quite impossible 

 to make use of them (Cohnheim). 



There is one other property peculiar to albuminoids which is also 

 conditioned by their anatomical character, and which makes the 

 description of albuminoids difficult namely, their * aging.' According 

 to Cohnheim cells are constantly renewed by their metabolism and 

 do not age. While thus cell-albumins and the soluble albumins remain 

 the same during the whole life of the animal, the ground-matrix 

 of connective tissues alters in a remarkable way with age ; it 

 increases in amount, becomes firmer and harder. This is specially 

 distinct in the connective tissue proper ; while young connective 

 tissue consists essentially of cells with only a little, soft ground- 

 matrix, it forms in older animals and also in scar tissues a coarse, 

 tough, firm mass, which has hardly a single feature in common with 

 the young tissue. Amongst other albuminoids analogous changes are 

 met with, so amongst the supporting structures and shells of inverte- 

 brates. The same tissue which while young is soft and pliable 

 becomes with advancing age, especially if lime is deposited, as hard 

 as stone. It is unknown to what extent the mature organs differ 

 chemically from the young tissue as regards the albuminoid radical, 

 for the percentage composition shows no distinct alterations, but 

 naturally the readiness with which a tissue passes into solution 

 diminishes as the tissue becomes harder ; collagen and elastin get to 

 resemble keratin, while their dissociation-products, their reactions, and 

 their composition remain the same as of old. A great many of the 

 contradictions of authors may be explained by taking into account the 

 age-differences of albuminoids (Cohnheim). 



The author wishes to point out that it is a great mistake to assume 

 that cells do not age, and that their metabolism keeps them eternally 

 young. If this were the case we ought, according to Cohnheim, only 

 to die because our blood-vessels and other connective tissues have 

 become old. That aging affects all the cells of the body has been 

 established by the author long ago, 1 and holds good for both vegetable 

 and animal cells. 2 The chief feature of advancing age is a diminu- 

 tion in the nuclear activity, i.e. of that very factor which normally 



1 Mann, Report of British Assoc. for Advanc. of Science, Edinburgh, 1892, p. 735. 



2 L. H. Huie, La Cellule, II. 83 (1895), (cells of Lilium Martagon). Hodge and 

 Mann (nerve-cells). 



