CHEMICAL BASIS OF THE ANIMAL BODY. 83 



that gelatin appears to be more readily metabolised than proteids, we may regard 

 gelatin as a valuable food-stuff, but not as a food which can supply the nitrogenous 

 needs of the tissues themselves. The facts thus stated may supply an explanation 

 of the beneficial effects which are supposed to result from the use of jellies in 

 training diets 1 . 



Chondrin. 



The matrix of hyaline cartilage is composed of an elastic, 

 semitransparent substance which is insoluble in cold or hot water 

 and does not swell up appreciably by treatment with either water 

 or dilute acetic acid. By prolonged treatment with water under 

 pressure in a Papin's digester it is gradually dissolved and yields a 

 solution which gelatinises on cooling and now contains the substance 

 usually spoken of as chondrin. The hyaline matrix of cartilage appears 

 thus to bear the same relationship to chondrin that the ground- 

 substance of connective-tissue (collagen) does to gelatin, and is therefore 

 frequently spoken of as 'chondrigen.' 



The substance known as chondrin, which is obtained in solution by 

 the action of superheated water on hyaline cartilage, exhibits the 

 following characteristic reactions 2 . It is precipitated by acetic acid 

 which does not, even if in considerable excess, redissolve the precipi- 

 tate ; minute quantities of mineral acids similarly cause a precipitate 

 to appear which is in this case readily soluble in the slightest excess of 

 the acids. These reactions suffice to distinguish between chondrin and 

 gelatin, and a further distinction may be made on the basis of the fact 

 that solutions of chondrin are precipitated by several reagents such as 

 alum, normal lead acetate, and other metallic salts (of Ag and Cu), 

 which yield no precipitate with gelatin, while on the other hand 

 mercuric chloride and tannin do not precipitate chondrin but are 

 characteristic precipitants of gelatin (see above). Chondrin is power- 

 fully laevorotatory ; in faintly alkaline solution (a) D = - 213*5 ; in 

 presence of excess of alkali this becomes (a) D = - 55*20 3 . 



By prolonged treatment with boiling water, or shorter heating 

 with dilute (1 p.c.) sulphuric acid or stronger hydrochloric acid, 

 chondrin is decomposed with the formation of a nitrogenous crystallis- 

 able product which characteristically reduces alkaline solutions of 

 cupric oxide 4 . Opinions however differ considerably as to the real 

 nature of this reducing substance. It was at one time regarded as a 

 true carbohydrate and more recently Landwehr has identified it with 



1 For a statement of the nutritional, metabolic and physiological significance of 

 gelatin see Hermann's Hdbch. d. Physiol. Bd. vi. Sn. 123, 318, 391, 395. 



2 Moleschott u. Fubini, Moleschott's Untersuch. Bd. xi. (1872), S. 104. 



3 de Bary, loc. cit. (sub gelatin). 



4 v. Mering, Inaug.-Diss. Strassburg, 1873. 



