The appearance of ammonia indicates the growth of proteolytic germs. Distil 50 c.c. of milk, 50 c.c. of neutral methyl alcohol, 10 Gin. NaC1, 0.5 Gm. from a 2 litre still, with 50 ann. pressure, for a quarter of an hour, in and titrate. Add 10 c.c. of 10 per cent. iodine trichloride solution to 10 c.c. of milk. To the filtrate add slowly filtered'3 per cent. lime water, until, a, black precipitate of nitro gen iodide appears, which is, however, dissolved by an excess of limo water.
Choice milk, when kept at 24° C. (75° F.) must show the original acidity after 12 hours, and 10 degrees at most after 24 hours. Ordinarily pure milk under the same conditions should not sour until after 24 hours.
Iii the ferment test, milk between 38° C. and 40° C. (100°-104° F.) is put in glasses that have previously been cleaned with the greatest, care. The expert, after a shorter or longer interval ascertains whether the organisms that produce latic acid, the butyric acid bacilli, or the proteolytic genus preponderate.
When a milk that has been impaired by proteolytic germs is freed from them by further pasteurization, it will disclose its condition to the expert. by taste, or, chemically, hy the indication of allnunoses and pep tones; hut, this important test has not vet been worked out. A micro scopical examination univ be made for dead germs.
Bacteriological investigation consists chiefly in counting the lique fying and non-liyusfying species. (In detail by H. Swithinback and C. Newmann, Bacterioloyy of Milk,l.ondon, 1903; H. W. Conn, Bacteria 'n Milk and Its Products, Philadelphia, 1903.) Choice milk, at the iliac of its delivery, without pasteurization, should contain at. the most 10,000 germs to the cubic centimetre; ordinary milk has as many as 200 millions.
With most diseases of the udder, scaly particles produced by the inflammation fall into the milk; these can naturally be found in un strained milk only. Abnormally low acidity, great fluctuations in elec trical conductivity, great depression of the freezing-point, and a sub normal index of refraction for the milk serum indicate an origin from diseased animals.
The proportion of fat can be determined most easily by the Reid butyromete•, which shows 0.2 per cent. more than analytic processes. Into this instrument --those with the plano-convex scale are the best— is placed first 10 c.c. of sulphuric acid of 1.825 specific gravity, then 11 c.c. of well mixed milk at about 15° C., (50° F.) and 1 c.c. of the purest. amyl alcohol at its boiling-point of 12S° C. to 130° C. (262°-266° F.) (in the vacuum test with water there should be no liberation); close with rubber stoppers and shake the butyrometer thoroughly, after winding a cloth around it, until no coagulation is visible. Centrifugate
either at once, or after the butyrometer, with the stoppers at the lower end, has been held for 10 minutes in a vessel filled with water heated to 60° C. (140° F.), in such a way that the entire scale remains under water. Bead at once from the scale the percentage of fat, making al lowance for the lower meniscus, while bringing the oil layer to the proper height by pressing in or screwing out the stopper. At the border line a clot sometimes separates, but, with proper centrifugation, this will be so fine that it will not disturb the reading. If you possess no cen trifuge, let the butyrometer stand at 60° C. (140° F.) for half an hour and repeat the process after 24 hours.
[The Babcock fat test is the one most commonly employed in the United States. This is simple and accurate, and has replaced most of the older methods. No expert chemical knowledge is required and only one chemical is used. A small hand centrifuge, using the regulation size test-bottles and especially adapted for the use of the physician, is on the market. The test is made as follows: 17.6 c.c. of the milk are drawn into a milk pipette and allowed to run into one of the test bottles. Smaller pipettes, holding one-fifth, one-fourth, one-third, or one-half of 17.6 c.c. are supplied when only a small amount of milk is available. Multiplying by the dilution will give the correct reading. 17.5 c.c. of clean sulphuric acid with a specific gravity of 1.082 are measured in the acid measure and slowly introduced into the test bottle. The milk and acid are thoroughly mixed in the bottle by a rotary motion, placed in the centrifuge, and whirled for 4 minutes. Boiling water is then added by means of the pipette until the lower part of the column of fat conies Nvithin the scale on the neck of the test-bottle. A second whirling for 1 minute completes the separation of the fat. The test comes out clearer and nicer, and the fat is kept more limpid, if boiling water is put in the cups which surround the bottles. The fat thus obtained should form a clear, yellowish liquid quite distinctly separated from the acid solution.] The proportion of alb can be calculated from the proportion of nitrogen in the tannin precipitation by multiplying by 6.37, from the proportion of nitrogen in the milk by multiplying by 6, or from the difference between the calculated proportion of solids and the known proportion of fat, sugar, and ash (about 0.71 in cow's milk). The de termination from the depth of the deposit which the Esbach solution produces in skimmed milk gives only approximate values, even when eentrifugated.