168 LABOR A TOR Y GUIDE IN PHYSIO LOG Y. 



(4) Fill a dialyzer with diluted milk one day before the 



demonstration. 

 J. Experiments and Observations. 



(1) What proportion of milk evaporates at the tempera- 

 ture above suggested ? It may be taken for granted 

 that this proportion represents practically the water 

 of the milk. 



(2) Of the solids of milk what proportion is organic and 

 what proportion is inorganic? 



(3) What bases predominate in the ashes? [Let a 

 student be assigned this problem for solution.] 



(4) What is the character of the organic constituents of 

 milk? 



(a) Note that the milk that has been standing has 

 separated into two layers, an upper yellowish layer 

 and a lower bluish white layer. 



(b) Draw off with pipette a few cubic centimeters 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 vigorously. Osmic 

 acid has the same effect upon the cream as upon the 

 olive oil. The cream is, in fact, fat in physiological 

 emulsion. Quantitative examination shows that 

 about 4% of milk or 4 13 of the solids of milk con- 

 sists 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% acetic acid while stirring with a 

 rod, until the casein separates as a copious flocculent 

 precipitate. After the casein has partially settled de- 

 cant off a few cubic centimeters of the supernatant 

 liquid and subject it to the Fehling test. The abun- 

 dant precipitate indicates the presence of a reducing 



