10 CHEMICAL PHYSIOLOGY. 



11. Diffusibility of Peptones. Place a solution of peptones in 

 a dialyser covered with an animal membrane, as directed in 

 Lesson I., 1, (A.), and test the diffusate after some time for 

 peptones. 



THE ALBUMENOIDS. 



12. I. Gelatin is obtained by the prolonged boiling of con- 

 nective tissues, and from the hypothetical substance " Collagen,^ 

 of which fibrous tissue is said to consist. 



Preparation of a Solution. Use commercial gelatin. Make a 

 watery solution by allowing it to swell up in water, and then 

 dissolving it with the aid of heat. 



(a.) It is insoluble, but swells up, in cold water. 



(b.) After a time heat the gelatin swollen up in water ;. 

 it dissolves. Allow it to cool ; it gelatinises. 



(c.) Precipitate separate portions by each of the following: 

 Mercuric chloride, tannin, alcohol, and platinic chloride. 



(d.) It is not precipitated by acids (acetic or hydrochloric), 

 or alkalies, or lead acetate. 



(e.) It is not precipitated by acetic acid and potassic 

 ferrocyanide (unlike albumin). 



(f.) It is not coagulated by heat (unlike albumin). 



(g.) It gives the xanthoproteic and biuret tests, and that 

 with Millon's reagent. It is precipitated by picric acid; 

 the precipitate is dissolved on heating, and reappears on 

 cooling. 



13. II. Chondrin is derived by prolonged boiling from the 

 matrix of cartilage, which is supposed to consist of the hypothe- 

 tical substance " Chondrogen." It seems to be really a mixture 

 of mucin and glutin. 



14. III. Mucin, see " Bile." 



