MEDICAL MILK COMMISSION'S 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 Gilded, 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 S0° 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 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 case 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 Ravencl. — 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 mnge from 
1.029 to 1.034. 
88. 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. 
