DIGESTION AND ABSORPTION. 169 



sugar. It is milk sugar lactose. About 4.4% of 

 milk or y$ of the solid matter of milk is lactose. 

 (fi) Wash the casein by the repeated addition of water, 

 followed by decantation; pour it into a linen sack 

 or a towel and press out the water; further extract 

 the water with absolute alcohol; extract the remnant 

 of fat with ether; dry in the air. The white granular 

 material that remains is nearly pure casein, the most 

 important proteid of milk, and represents nearly 4% 

 of milk. 



(7) Heat 100 c. c. of the fresh milk in a beaker. Before 

 the boiling point is reached a membrane gathers upon 

 the surface of the milk. This membrane represents 

 the lact-albumin of the milk, which has been coagu- 

 lated by the heat and has collected in the membranous 

 coagulum at the surface. The lact-albumin repre- 

 sents only a small proportion of the milk proteid. 



(8) To 30 c. c. of fresh milk in a beaker add common 

 salt to saturation. Record results. 



(9) To 30 c.c. of fresh milk in a beaker add magnesium 

 sulphate to saturation. Record results. 



(10) Dilute fresh milk to one-fifth normal and subject it 

 to the following tests, recording results: 



(#) The iodine test. 



(^) Tromer's test. 



(V) The xanthoproteic test. 



(//) The Biuret test. 



(>) The picric acid test. 



(/) The absolue alcohol test. 



() The osmic acid test. 



(11) Fill a dialyzer with the diluted milk. One day 

 later examine the diffusate: 



{a) For any of the inorganic constituents of milk. 

 (/>) For the carbohydrate constituents of milk. 



