556 CHEMISTRY OF THE PROTEIDS CHAP. 



brings about the synthesis of the simple ammo-acids into the higher 

 compounds according to the author's view. The cell bodies show with 

 advancing age a diminishing affinity for basic dyes and a great 

 diminution in the size of the nucleoli. As shown above, Cohnheim 

 assumes that all albuminoids undergo a spontaneous change, quite 

 irrespective of cell activity, but this again does not bear out the author's 

 histological experience. Whenever a change occurs, e.g. in cartilage, 

 it is always in connection with and in close proximity to the nucleus. 

 The hardening of connective tissues, brought about by a deposit of 

 lime-salts, depends primarily on the excretion of phosphoric acid by 

 the nucleus or the synthesis of cbondro-sulphuric acid in the imme- 

 diate neighbourhood of the nucleus, and therefore depends on the cell. 

 When again elastin during advancing age is changed into elacin (Unna), 

 when all its staining reactions become altered, we may assume a spon- 

 taneous change of elastin into elacin, but with equal right we may 

 hold that with advancing age certain substances circulating in the 

 body are deposited in the elastin and thereby change its staining 

 reactions. To compare immature growing connective tissue with 

 fully formed and aged tissue, as Cohnheim has done, is hardly per- 

 missible, for judging by micro-chemical data, there is no difference 

 between ' young ' (but not that in statu formandi) and ' adult ' white 

 fibrous tissue. Experimental investigations have further shown, as 

 already pointed out, that the white fibrous tissue is drawn upon during 

 states of inanition, i.e. that it is constantly changing within certain 

 limits. 



1. Collagen. Gelatine 



Collagen. The fibrils of ordinary white fibrous tissue, the ground 

 substance of bone and of cartilage, are composed of 'glue-yielding 

 tissue ' or collagen. When collagen is treated with boiling water 

 it passes into solution, and to this dissolved collagen the terms 

 gelatine, glutin, or glue are given. The most important property of 

 gelatine consists in it turning into a jelly at room-temperature, becom- 

 ing fluid on being heated, and again solidifying on cooling, and 

 so on. 



Collagen is but little understood for the reasons given above. 

 Kiihne and Ewald x have shown that collagen of the ordinary connec- 

 tive tissue is very easily attacked by pepsin + hydrochloric acid, while 

 it is not attacked by tryptic digestion. Connective tissue may, therefore, 

 be obtained in a pure state by removing ' all other albuminous sub- 



1 A. Ewald and W. Kiihne, Verhandl. d. naturh.-med. Vereines Heidelberg, New 

 Series I. S. 451 (1876) ; A. Ewald, Zeitschr. f. Biol. 26. 1 (1890). 



