EXAMINATION AND ANALYSIS OF MILK It will not take the physician long to determine from what animal a given milk is derived. By Steinegger's method, which is given below, an addition of as little as 13 per cent. of goat's milk to cow's milk will be detected. Milk not Over 24 hours old is to have its cream removed by centrifugation. Then 100 c.c. of the skim milk is to be heated to C. (122° F.) and combined with 10 c.c. of 25 per cent. ammonia water, and is to be kept at this temperature and mixed half hourly. After an hour and a half it must again be centrifugated. Within from 2 to 3 hours a precipitate of albumin will have formed in the goat's milk. One way in which human milk may he distinguished from cow's milk is by the reaction. Heat 5 c.c. of milk with 2.5 c.c. of 10 per cent. ammonia to 00° C. (110° F.) for a quarter of an hour. Human milk turns violet-red; cow's milk, if it does not contain formaldehyde, turns yellow. With other kinds of milk the biological test is more relial de.
The Amount of Dirt —Add drops of formnlin to every 100 c.c. of milk and let it stand in a beaker, or in a bottle with a graduated strainer (Gerber, Zurich); or •entrifugate it either in ordinary vessels or in those described by Thorner; or strain it in definite quantities through very fine bolting-cloth or through cotton-wool filters. The thickness of the layer of con on-wool is very important. Either read off the height of the layer on the graduated scale or dry the refuse and weigh it. Choice milk must not contain any. For ordinary milk, from 5 to 10 ing, per litre may be allowed. Ilenkel's apparatus for estimating the dirt is made in the form of a filter. The tin cylinder used for intro ducing the milk is bent inward at the bottom so that a part of the cotton-wool layer is perfectly protected from the dirt, and this white surface (b) serves as a standard of comparison. On an ordinary till can (c) is set a pan with a perforated bottom (d), on which the layer of cotton-wool (e) lies, and on this the cylinder (a) is placed and held fast by a tin clamp (f). Before the milk is poured in, the perforated tin disk (g), with the strip of tin attached, is init on to prevent the layer of cotton-wool from being worn and is re moved immediately after. In comparing
this with Fliegel's tester, beside the pro tected surface of the filtering-layer, there is the advantage that dirt cannot accumulate on the bottom of the cylinder above and so cannot penetrate to the cotton. Pour in 1 litre.
Freshness and Keeping Qualities of Milk.
—Experts can judge the freshness by the taste. Milk of 11 degrees of acidity and up wards (see below) coagulates in boiling.
Milk of S degrees or more shows coagulation when combined with an equal volume of 68 per cent. alcohol which does not give an acid reaction (the Martiny alcohol test); milk of 71 degrees does the same by the addition of an equal volume of 70 per cent. alcohol. Titrate 50 c.c. in a flask, adding 2 c.c. of a 2 per cent. alcoholic solution of phenolphthalein with one-fourth normal sodic hydrate solution (Soxhlet-Henkel), using at the same time the opposite test, with the same quantity of phenolphthalein, in a flask of the same shape, without water, and on a white bottom. The titration is success ful as soon as the sample turns light pink after a thorough shaking. Double the number of cubic centimetres of sodic hydrate solution is what is called a degree of acidity. ' Titration with NaOH of one-tenth normal strength, because of the larger amount of water, gives less than value (for example, S:15 instead of S: 3S). The limits, in normal milk, range between 7 and S.5, but values over S are suspicious. Values be low normal are obtained when alkalies are added and in most diseases of the udder (for example, tuberculosis of the udder); values above normal, outside of acidification, are obtained from biestings and par ticularly in jaundice.
Add to 0.1 c.c. of milk 3 drops of the following mixture: 1.0 methy lene blue. 20.0 absolute alcohol, 20.0 distilled water. Take 1 c.c. of this mixture to 250 c.c. of a sterilized physiological solution of common salt and keep the sample at 37° C. (98.6° F.). It should not lose its color entirely within two hours, as otherwise it is too strongly infected with vitiating bacteria.