Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER IV. COMPOSITION AND PROPERTIES OF CASEIN. Casein, the chief and characteristic albuminoid substance in milk, was, on account of its acid properties, long regarded as an albuminate, and was classed along with the alkali albuminates obtained by denaturing other albuminoid substances. Hoppe-Seyler, and more particularly Hammar- sten, were the first to demonstrate its separate entity, with a composition varying according to the originating animal. The casein of cows' milk consists of C, 52'96 per cent.; H, 7'04 to 7'53; N, 15'60 to 15'91; O, 22'78; S, 0'758 to 0'82; and P, 0'8 to 0'847 per cent. It is lacking in glycocoll and the carbohydrate group, but has a large proportion of tyrosin and tryptophane. Accordingly, it is readily decompqsed by pepsin and trypsin, and does not furnish any hetero-albumose on peptonisation. As the sole native albumen, it is also attacked by erepsin. Owing to the ease with which it is decomposed, casein also plays a special part in metabolism. The proportion of lysin and glutaminic acid is particularly high; and according to Wildenow and Salkowski, paranucleic acid contaminated with albumen contains 3 to 4 per cent, of phosphorus. The salts of casein are specially important; and, though like all albuminoids, it can form compounds with acids, and is therefore readily soluble in an excess of acid, its own acid characteristics are predominant. According to Lacqueur and Sackur, the equivalent molecular weight of casein in its compoundswith bases is 1,135, and its basicity is 4 to 6. The far higher molecular weights of 5,000 to 6,000, found by Salkowski, Hammarsten, Lehmann, Hempel and Soeldner, are based partly on hydrolysis and partly on the investigation of acid salts. Soeldner differentiates between two series of salts, Courant three...