A manual of practical hygiene / by Edmund A. Parkes ; edited by F.S.B. Francois de Chaumont.

Date:
1887
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Licence: Public Domain Mark

Credit: A manual of practical hygiene / by Edmund A. Parkes ; edited by F.S.B. Francois de Chaumont. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

    775/838 (page 723)
    Infusona are sometimes found in milk, and funcji {O'idmm lactis and Fenicillium) are so almost invariably, if the milk has been kept.i Scheme for a Short Examination. As a medical officer is constantly called upon to examine milk, and will seldom have time to go thoroughly into all the points just noted, the foUow- • ing short scheme will be useful :— 1. Put some milk into the long graduated glass for deposit, and for deter- mining percentage of cream.^ 2. Take physical characters, reaction, and specific gravity. Take specific gravity of the whey, if there be time to do this. 3. Determine fat by Vogel's milk-test.^ Other plans of examination are recommended, such as the Lactobutyrometer of Marchand, and the Lacto- crite, but those apparatus are not likely to be in the hands of medical officers. 4. Examin3 the milk with the microscope. The compainson of the specific gravity, and L' le amount of cream which rises, or of fat, will be found to give, in conjunctii .i with the physical characters, a very good idea of the quality of the milk. Adulterations. 1. Water.—This is extremely common, and is, in fact, generally the only adulteration; it is best detected by specific gravity or by the amount of solids by evaporation. Wanklyn suggests the amount of ash as a good test of watering; the normal ash being, according to him, about 0'73 per cent. In this case the calculation would be as follows :—Let (a) be the observed percentage of ash and (A) the normal amount: then 100 — 122^ = A per cent, of water added: let (a) =0'50, and A = 0-73: then 100 —'^^^^yg— =31-5 per cent, of water added. In a similar way the amount of solids not fat may be used as a standard. 2. Starch, dextrin, or gum, to conceal the thinness and the bluish colour produced by water. Not a common adulteration. Add iodine at once for starch; boil with a drop of acetic acid, and add iodine for dextrin, or add acetate of lead and then ammonia: a white precipitate falls. 3. Annatto or turmeric is added to give colour. Liquor potassse at once detects turmeric. 4. Emulsions of seeds {hemp or almond), added ; this is uncommon. Boil. The albumen of the seeds coagulate ; the milk will not mix with tea. Hemp seed gives an unpleasant odour to the milk (Normandy). 1 Dr Willard, of Comell University, notes the experience of Professor Law, who observed a peculiar ropy material in milk, and traced it to cows drinking stagnant water containing organisms similar to those found in the milk ; a drop of this water, put into good milk, soon developed these organisms. The cows were feverish.—(Dr John Ogle, Journal of the Af/rirultural Society, Nov. 15, 1872 ; Lancet, Oct. 11,1873.) 2 Macnamara (Indian Medical Gazette, 1873) finds that the cream is not very useful in India as a test, the rapid coagulation of the milk preventing it rising. The addition of ammonia, as recommended by Adams, might obviate this. Similarly Vogel's test does not give satis- factory results. It would, therefore, be necessnry to determine the constituents by the chemical methods if possible. The following plan may be adopted:—Measure out carefully two ])ortions of milk, and evaporate both to dryness : weigh : from this the total solids may be obtained : then incinerate one portion : weigh : this gives the ash. Exhaust the other with ether in Gerber's or Soxhlct's apparatus : from this the fat may be obtained. (The sample dried for fat had better bo mixed with plaster, or soaked up with bibulous paper in Adams' way.) Exhaust the residue with alcohol; this gives the lactin, which may be deter- mined either by weighing or incineration, or by Fehling's process ; weigh the residue, then incinerate it, and weigh again : the difference will be the casein. The last weighing also gives a controlling determination of the ash.