320 PHYSIOLOGICAL CHEMISTRY 



the film now form? Of what substance is this film composed? The biuret test 

 was positive ; why do we not get a coagulation here when we heat to boiling? 



6. Coagulation Test. Place about 5 c.c. of milk in a test-tube, acidify slightly 

 with dilute acetic acid and heat to boiling. Do you get any coagulation? Why? 



7. Action of Hot Alkali. To a little milk in a test-tube add a few drops of 

 potassium hydroxide and heat. A yellow color develops and gradually deepens 

 into a brown. To what is the formation of this color due? (See Moore's Test, 

 Chapter II.) 



8. Test for Chlorides. To about 5 c.c. of milk in a test-tube add a few drops 

 of very dilute nitric acid to form a precipitate. Filter off this precipitate and test 

 the filtrate for chlorides. Does milk contain any chlorides? 



9. Guaiac Test. To about 5 c.c. of water in a test-tube add 3 drops of 

 milk and enough alcoholic solution of guaiac (strength about i : 60) 1 to cause 

 turbidity. Thoroughly mix the fluids by shaking and observe any change which 

 may gradually take place in the color of the mixture. If no blue color appears 

 in a short time, heat the tube gently below 6oC. and observe whether the 

 color reaction is hastened. In case a blue color does not appear in the course 

 of a few minutes, add hydrogen peroxide or old turpentine, drop by drop, until 

 the color is observed. 



Fresh milk will frequently give this blue color when treated with an 

 alcoholic solution of guaiac without the addition of hydrogen peroxide 

 or old turpentine. Those milks which respond positively, fail to do so 

 after boiling 15-20 seconds. What substances beside milk respond to 

 this test? See discussion on page 258. 



10. Differentiation of Human and Cow's Milk (Modification of Bauer's Test) 2 . 

 Introduce 2 c.c. of fresh human milk into a 50 c.c. test-tube and 2 c.c. of fresh 

 cow's milk into another similar tube. Add to the contents of each tube i drop of 

 a 0.25 per cent aqueous solution of nile-blue sulphate (Griibler). Shake the 

 tubes gently and permit them to stand undisturbed for 10-30 minutes. The 

 milk assumes a bluish cast in each case. At the end of the lo-minute interval 

 add lo c.c. of ether to the contents of each tube and shake very thoroughly for one 

 minute. The ether extracts the pigment from the human milk, leaving the milk 

 white. In the case of cow's milk the ether does not extract the dye and the milk 

 remains bluish in color. 



11. Tests to Differentiate between Raw Milk and Heated Milk. 



(a) Trikresol Peroxidase Reaction (Kastle) . The peroxidase reaction of 

 milk is founded upon the fact that small amounts of raw milk will in- 

 duce the oxidation of various leuco compounds by hydrogen peroxide. 

 This reaction has been used in a practical way as the most convenient 

 means of differentiating between raw milk and heated milk. Many 

 substances have been employed for this purpose, e.g., guaiac, para- 

 phenylenediamine, ortol, amidol, etc. Kastle has found that a dilute 



1 Buckmaster advises the use of an alcoholic solution of guaiaconic acid instead of an 

 alcoholic solution of guaiac resin. Guaiaconic acid is a constituent of guaiac resin. 



2 Bauer: Monatssch. f. Kinderheil., n, 474, 1912-13. 



