﻿MEDICAL MILK COMMISSIONS AND CERTIFIED MILK. 35 



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, Barthel ; 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 commission 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 — Storch'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 t~<lded, 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 be- 

 comes, 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 S0° 

 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 guaiac 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 guaiac 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 ease of milks which have been heated to 176° F. or 80° C. 

 (Jensen's Milk Hygiene, Pearson's translation, p. 192.) 



Microscopic test for heated (pasteurized) milk — Frost and Ravenel. — 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 Chap- 

 man air pump. Only about 2 mm. of milk are left above the sediment which is 

 in the bottom of the sedimentation 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 gravity. — The specific gravity of certified milk shall range from 

 1.029 to 1.034. 



8S. The specific gravity shall be determined at least each month. 



The Quevenne lactodensimeter is recommended for the determination of the 

 specific gravity. It is made like an ordinary aerometer and divided into degrees 

 which correspond 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 lengthening the instrument. From such a lactoden- 

 simeter one can easily read off four decimal places. 



The milk the specific gravity of which is to be determined is well shaken and 

 poured into a high glass cylinder of suitable diameter ; the aerometer is dropped 

 in slowly, in order to prevent its bobbing up and down. (The bulb should be 

 free from adhering air bubbles.) The figures on the stem are the second and 

 third decimals of the numbers of the specific gravity, so that 34 is to be read 

 1.034. For this examination, the temperature of the milk must be 15° C. 



