16 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



without filtering. 1 100 to 200 cc. of milk 2 are heated in a 

 beaker to 40, 5-10 cc. of the rennin solution added and well 

 stirred. Coagulation soon takes place. The coagulum, con- 

 sisting of casein and fat, gradually separates, leaving a fluid 

 containing albumin and sugar (milk-serum or sweet whey). 

 The process is perfectly analogous to the coagulation of blood 

 with the formation of the blood-clot and separation of the 

 blood-serum. The casein differs somewhat in its properties 

 from the casein precipitated by acids. We therefore give it 

 the name paracasein or cheese. Let stand till next day, then 

 pour off as much of the fluid as possible, grind the coagulum, 

 the cheese, with water, filter, wash again with water, and press 

 the cheese dry between folds of muslin. In order to remove 

 most of the fat we proceed in the same manner as given under 

 Casein. When washed a few times with ether the paracasein 

 is almost free from fat. 



The paracasein like the casein dissolves readily in lime- 

 water as well as in water to which sodium hydroxide or sodium 

 carbonate solution has been added. It is reprecipitated on 

 the addition of acetic acid. When ground with water and 

 calcium carbonate the paracasein does not dissolve as readily 

 as the casein. The paracasein always contains calcium ; solu- 

 ble calcium salts are essential for the coagulation of milk by 

 rennin (Hammarsten). The sweet whey gives the guaiacum- 

 turpentine reaction, and when heated it forms a voluminous 

 precipitate of albumin. 



If we add to 100 cc. of milk 5 cc. of a 1 per cent, solution 

 of sodium oxalate, then the rennin ferment and heat to 40^ 

 the milk does not coagulate on account of the precipitation 

 of the calcium as calcium oxalate. If, however, we add a 



1 The solution appears to be more active when twenty-four hours old 

 than when freshly prepared. 



2 Preferably skimmed milk. 



