CASEIN. 377 



different observers. Casein appears to us to be a highly transmut- 

 able substance, often undergoing change on the application of the 

 mildest reagents. In a word, a method of preparing casein, which 

 would exclude all suspicion of its being changed by the process, is 

 still a desideratum. The circumstance that the elementary ana- 

 lyses of the separated matters give such slightly different results, 

 adds very much to our difficulty of ascertaining whether the con- 

 stitution of casein is simple or complicated. 



Casein, when thoroughly coagulated by rennet, and purified, 

 is hard, and presents a yellowish translucent appearance; it softens 

 and swells in water, but is insoluble both in that fluid and in 

 alcohol. Like its soluble modification it combines with adds and 

 alkalies ; but on separating the inorganic part from the casein, the 

 latter is insoluble in water. In its relation to the stronger mineral 

 acids it in every respect resembles coagulated albumen ; it is as 

 difficult of solution in acetic acid as its soluble modification ; 

 alkalies dissolve it very readily, and, if concentrated, decompose it 

 like the other protein-compounds on the application of heat. On 

 heating casein, it softens, may be drawn out in threads, and becomes 

 elastic; and at a higher temperature it fuses, swells up, carbonises, 

 and developes the same products of distillation as albumen and 

 fibrin ; when strongly heated in the air it burns with a flame, and, 

 unless carefully washed with acidulated water, leaves an ash con- 

 taining carbonate and phosphate of lime, but no alkali. 



The investigations of lljenko* show that casein during its putre- 

 faction, (even when perfectly freed from fat) developes at first 

 carbonate of ammonia and hydrosulphate of ammonia, but that, 

 after a space of from two to five months, its principal products are 

 ammonia, valerianic acid, butyric acid, and leucine, and to these 

 substances Boppt adds a white, crystallisable, sublimable body, 

 having a very strong feecal odour, and an acid which, when decom- 

 posed with a mineral acid, yields a brown substance together with 

 tyrosine, and ammonia. On fusing casein with hydrated potash, it 

 developes a very large quantity of hydrogen and ammonia, leaving 

 much valerianic acid in combination with the potash, and likewise 

 leucine and tyrosine. (Liebig.^:) When decomposed with chromic 

 acid, or with sulphuric acid and binoxide of manganese, casein yields 

 much more acetic acid, oil of bitter almonds, and ben zoic acid, but 

 much less valerianic acid and butyric acid than fibrin ; in reference 

 to the quantities of these products of decomposition it most nearly 



* Ann. d. Ch. u. Pharm. Bd. 55, S. 78-95, and Bd. 58, S. 264-273. 

 t Handworterb. der Chemie v. Liebig, Wohler u. Fogg. Bd. 3, S. 220. 

 Ann. d. Ch. u. Pharm. Bd, 57, S. 127-129. 



