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 sub- 

 stances. 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, 2278; S, 0758 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. Ac- 

 cordingly, it is readily decomposed 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 character- 

 istics are predominant. According to Lacqueur and Sackur, 

 the equivalent molecular weight of casein in its compounds 



(31) 



