166 SPECIAL PHYSIOLOGY 



two layers, an upper yellowish layer and a lower bluish-white 

 layer. 



(6) Draw off with pipette a few cubic centimetres of the cream and 

 in a test-tube add an equal volume of osmic acid. To a few drops of 

 olive oil in another tube add osmic acid. Shake both tubes vigor- 

 ously. Osmic acid has the same effect upon cream as upon olive oil. 

 The cream is, in fact, fat in physiological emulsion. Quantitative 

 examination shows that about 4 per cent, of milk, or ^ of the solids 

 of milk, consists of fats in which olein predominates. 



(5) Fill a siphon with water and introduce it through the cream to 

 the bottom of the 500-c.c. cylinder; draw off 300 c.c. of the milk; 

 add to it four volumes of water; slowly add 1 per cent, acetic acid, 

 while stirring with a rod, until the casein separates as a copious 

 flocculent precipitate. After the casein has partially settled, decant 

 off a few cubic centimetres of the supernatant liquid and subject it 

 to the Fehling test. The abundant precipitate indicated the pres- 

 ence of a reducing sugar. It is milk-sugar lactose. 



(6) 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 per cent, 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 lactalbumin of the milk, which has 

 been coagulated by the heat and has collected in the membranous 

 coagulum at the surface. The lactalbumin represents only a small 

 proportion of the milk proteid. Subject the membrane to the xantho- 

 proteic test or the Millon test to demonstrate that it is a proteid. 



(8) To 30 c.c. of fresh milk in a beaker add common salt to satura- 

 tion. 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: 



(a) Tromiher's test. 



(b) The xanthoproteic test. 



(c) The biuret test. 



(d) 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. 

 (6) For the carbohydrate constituents of milk. 



(c) For the proteid constituents of milk. 



(d) For the fatty constituents of milk. 



