416 CONSIDERATION OF CARBON COMPOUNDS. 



is, when recently obtained, a white, gelatinous, tenacious mass, con- 

 sisting of numerous minute fibrils. When dried it becomes hard 

 and brittle. It is insoluble in water, alcohol, and ether, but swells 

 up and dissolves slowly in dilute acids. 



b. Vegetable fibrin or Gluten exists in many parts of vegetables, 

 and is best obtained from wheat-flour by kneading it on a sieve with 

 water, when the starch passes through and gluten remains as a soft, 

 elastic mass, insoluble in water, alcohol, and ether. It is probably a 

 mixture of several proteids. 



Class V. Coagulated proteids. These are formed by the action 

 of heat, acids, alcohols, etc., on solutions of true albumins or globu- 

 lins. They are insoluble in water, dilute acids and alkalies, as also 

 in neutral salt solutions of any strength. In fact, they are soluble 

 only in strong acids and strong alkalies, when, however, a destructive 

 decomposition takes place. Prolonged contact with dilute acids, 

 especially at high temperatures, also effects a partial solution with 

 decomposition. The most characteristic property of coagulated pro- 

 teids is that they readily undergo gastric and pancreatic digestion. 



Class VI. Albumoses. Intermediary products between acid- 

 albumins and the peptones. The albumoses are at least three in 

 number : protalbumose, hetero-albumose and dextro-albumose. The 

 albumoses are precipitated by a saturated solution of ammonium sul- 

 phate, while peptone remains in solution. All are soluble in dilute 

 solution of sodium chloride, and some in water. They differ but 

 slightly from one another, and give a red color with the biuret test. 



Class VII. Peptones. These are the products of the action of 

 the gastric and pancreatic juices upon proteids during the process of 

 digestion. They are soluble in water, acids, alkalies, salt solutions, 

 including solution of ammonium sulphate; only precipitated by 

 alcohol, tannic acid, potassium mercuric iodide, and mercuric chlo- 

 ride. They give a red color with the biuret test. Characteristic is 

 that peptones are capable of dialysis, or of diffusion through mem- 

 branes, whilst proteids are not. 



Class VIII. Amyloid substance or Lardacein. This is a 

 pathological product, which is sometimes found in severe wasting 

 diseases, imparting a peculiar translucent appearance to the tissues. 

 Its composition is that of the proteids, but differs from them in being 



