268 Principles of Legislative Milk Control. 



is again' added, and the liquid shaken out with small quantities of ether. On evapora- 

 tion of the ether, the benzoic acid is left behind in almost pure state, the only impuri- 

 ties being small quantities of fat or ash. 



The benzoic acid which is obtained is dissolved in a small quantity of warm 

 water, a drop of sodium acetate and neutral ferric chloride added, and the red precipitate 

 of benzoate of iron indicates the presence of the acid. (Milk and Dairy Products, Bar- 

 thel; translated by Goodwin, p. 121.) 



85. Detection of heated milk. Certified milk or cream shall 

 not be subjected to heat unless specially directed by the commis- 

 sion to meet emergencies. 



86. Tests to determine whether such milks and creams have 

 been subjected to heat shall be applied at least once each month. 



Detection of "heated milk. Starch's method. Five cubic centimeters of milk are 

 poured into a test tube; a drop of weak solution of hydrogen dioxide (about 0.2 per 

 cent) which contains about 0.1 per cent sulphuric acid, is added, and two drops of a 

 2 per cent solution of paraphenylendiamin (solution should be renewed quite often), 

 then the fluid is shaken. If the milk or the cream becomes, at once, indigo blue, or the 

 whey violet or reddish brown, then this has not been heated or, at all events, it has not 

 been heated higher than 78 C. (172.5 F.); if the milk becomes a light bluish gray 

 immediately or in the course of half a minute, then it has been heated to 79 to 80 C. 

 (174.2 to 176 F.). If the color remains white, the milk has been heated at least to 80 

 C. (176 F.). In the examination of sour milk or sour buttermilk, lime water must be 

 added, as the color reaction is not shown in acid solution. 



Arnold's guaiac method. A little milk is poured into a test tube and a little 

 tincture of guaiae is added, drop by drop. If the milk has not been heated to 80 C. 

 (176 F.) a blue zone is formed between the two fluids; heated milk gives no reaction, 

 but remains white. The guaiae tincture should not be used perfectly fresh, but should 

 have stood a few days and its potency have been determined. Thereafter it can be 

 used indefinitely. These tests for heated milk are only active in the case of milks 

 which have been heated to 176 F. or 80 C. (Jensen's Milk Hygiene, Pearson's transla- 

 tion, p. 192.) 



Microscopic test for heated (pasteurised) milk Frost and Eavenel. About 15 c. c. 

 of milk are centrifuged for 5 minutes, or long enough to throw down the leucocytes. 

 The cream layer is then completely removed with absorbent cotton and the milk drawn 

 off with a pipette, or a fine-pointed tube attached to a Chapman air pump. Only 

 about 2 mm. of milk are left above the sediment which is in the bottom of the sedimen- 

 tation tube. 



The stain, which is an aqueous solution of safranin 0, soluble in water, is then 

 added very slowly from an opsonizing pipette. The important thing is to mix stain and 

 milk so slowly that clotting does not take place. The stain is added until a deep 

 opaque rose color is obtained. After standing 3 minutes, by means of the opsonizing 

 pipette, which has been washed out in hot water, the stained sediment is then transferred 

 to slides. A small drop is placed at the end of each of several slides and spread by 

 means of a glass spreader, as in Wright's method for opsonic index determinations. 



In an unheated milk the polymorphonuclear leucocytes have their protoplasm 

 slightly tinged or are unstained. 



In heated milk the polymorphonuclear leucocytes have their nuclei stained. In 

 milk heated to 63 C. or above, practically all of the leucocytes have their nuclei 

 definitely stained. When milk is heated at a lower temperature the nuclei are not all 

 stained above 60 C. The majority, however, are stained. 



87. Specific qravity. The specific gravity of certified milk 

 shall range from 1.029 to 1.034. 



88. The specific gravity shall be determined at least each 

 month. 



The Qnevenne lactodensimeter is recommended for the determination of the specific 

 gravity. It is made like an ordinary aerometer and divided into degrees which corres- 

 pond to a specific gravity from 1.014 to 1.040, or only 1.022 to 1.038, since by the latter 

 division a greater space is gained between the different degrees without unduly lengthen- 

 ing the instrument. From such a lactodensimeter one can easily read off four decimal 

 places. 



