CONSTITUENTS OF PLANTS, ETC. 339 



468. Albumen. If in the process for obtaining starch de- 

 tailed in 449, after the starch is settled you decant the 

 water from the vessel and boil it, it will become turbid, and 

 on standing will deposit a flocculent precipitate. This is 

 vegetable albumen, which has properties similar to those 

 of animal albumen, a common specimen of which we have 

 in white of egg. The precipitate above spoken of is essen- 

 tially the same as the white of egg coagulated by heat. 

 This albumen, which is thus found to be present in a small 

 amount in the grain of wheat, is very widely diffused in 

 the vegetable world. It is this substance in the sap of 

 wood which renders it so liable to decay. 



469. Casein. Vegetable casein is so called from its re- 

 semblance to the cheese contained in milk. It is found 

 chiefly in the seeds of leguminous plants, and therefore is 

 sometimes called legumin. Like gluten and albumen, it 

 contains nitrogen. It differs from albumen in not being 

 coagulated by heat ; but it is coagulated by acids, as is the 

 case with the cheesy matter or casein in milk. It may be 

 obtained from pease by the following process : Put a hand- 

 ful of pease into a vessel containing considerable water, and 

 let it stand for several days in a warm place. A great part 

 of the water will be absorbed by the pease, so that they will 

 become large and soft. Mash them, and add sufficient wa- 

 ter to make a thin paste. By treating this as the paste of 

 flour was treated in 449, you obtain the same substances, 

 viz., the gluten on the cloth, the starch deposited from the 

 liquid, and the albumen coagulated in the boiling of the 

 decanted liquid. If now, after separating the albumen from 

 the liquid by filtering, you add to the liquid a little acid 

 of some kind, a flaky white substance will be precipitated, 

 which is casein. 



470. Protein Substances. The three nitrogenous sub- 

 stances which we have thus briefly noticed albumen, fibrin, 



