XI 



THE ALBUMINOIDS : COLLAGEN 557 



stances by trypsin. While normal white fibrous tissue is not attacked 

 by trypsin, it is readily digested if it be allowed to swell in acids, and 

 if it be made to contract again by being heated up to 70 in water. 

 If the contraction is not allowed to take place, the connective-tissue 

 fibrils remain unaltered on being treated with trypsin. If white 

 fibrous tissue, made digestible by being boiled with water, is acted 

 upon by chrome-compounds, and is then exposed to light, it becomes 

 indigestible for both peptic and tryptic digestion. The insolubility 

 of chrome-gelatine induced by exposure to light is made use of in the 

 carbon-process of photography. 



In ordinary tendons, but also in yellow tendons, such as the- 

 ligamentum nuchse, white fibrous tissue occurs as fibrils along with 

 yellow fibrous tissue, composed of elastin, and along with mucin. The 

 behaviour of these collagen-fibrils towards digestive enzymes has been 

 very thoroughly investigated by Ewald, 1 who found them to react as. 

 does ordinary white fibrous tissue, but the collagens of different 

 animals differed considerably as regarded digestibility. Different 

 varieties of collagen will be mentioned later. 



Collagen gives rise to gelatine under different kinds of treatment,, 

 but most readily on being boiled with acids, although prolonged 

 boiling with water will also render collagen soluble. The time 

 required for changing collagen into gelatine varies greatly according 

 to the collagen under examination. 



Morner 2 found the collagen of fish-scales much more readily soluble 

 than that of the ordinary connective tissues of cartilage and bone. 

 Sadikoff 3 could obtain gelatine from the cartilage of the trachea of 

 the ox or the nasal cartilages of the pig by mere heating on a water- 

 bath, while the ear-cartilage of the pig required to be heated to 110. 



Hofmeister 4 believes the conversion of collagen into gelatine to 

 depend on a hydrolytic dissociation. 



GelatiM. Grlue or gelatine in a dry purified state forms a 

 colourless, amorphous powder, but the commercial gelatine occurs in 

 the shape of glassy plates containing water. Gelatine has been 

 frequently investigated because it is so readily accessible, but the 

 analyses of different observers do not agree very closely. Tire 

 probable reason for this divergence is that the collagen-fibrils always, 

 occur mixed up with other tissue constituents, which are also rendered 

 soluble when white fibrous tissue is boiled, and it is very difficult to. 



n A. Ewald, Zeitschr. f. Biologic, 26. 1 (1890). 



2 C. T. Morner, Zeitschr. /. physiol. Chem. 24. 125 (1897). 



3 W. S. Sadikoff, ibid. 39. 411 (1903). 



4 F. Hofmeister, ibid. 2. 299 (1878). 



