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Encyclopedia Britannica - Main :: MIC-MOL |
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MILK (0. Eng. meoluc; from a common Indo-European root, cf. Lat. mulgere, Gr. ?t dXyetv) , the fluid secreted by the mammary glands of the division of vertebrate animals called Mammalia (see MAMMARY GLAND), and primarily devised for the nourishment of their own young. The milk of various domesticated animals is more or less used by man for food. The milk of the cow, which may be taken as typical of all others, and is indeed by far the most important and valuable of all (see DAIRY AND DAIRY FARMING), is, when newly drawn
of fatty globules (cream) in a watery alkaline solution of casein, and a variety of sugar, peculiar to milk, called lactose. The fat (which when separated we know as butter) and the lactose constitute the carbonaceous portion of the milk regarded as food. The casein, which forms the principal constituent of cheese, and a certain proportion of albumen which is present, form the nitrogenous, while the complex saline substances and water are the mineral
Cow. Goat. Ewe.' Mare. Ass. Human. C o 1 8 O (1 C .~ boa cam) 0 V t, m~ a 8 E U Water. 86.87 87.00 84.48 83.70 90.310 91.65 88.02 3'50 4.00 6.11 4.45 1.055 0.11 2.90 Fat . .i 4.75 4 .10 3.94 5.16 1.953 P82 1.6o n an. d Casein and Sugar . . 4.00 4.28 4.68 5'73 6.285 6o8 7.03 Ash . . 0.70 0'62 0.79 0.96 0.369 0'34 0.31 In addition to these constituents milk contains small proportions of the gases carbonic acid, sulphuretted hydrogen, nitrogen and oxygen, and minute quantities of other principles, the constant presence and essential conditions of which have not been determined. These consist of galactin and lactochrome, substances peculiar to milk, discovered by Winter Blyth, with certain animal principles such as leucin, pepton, kreatin, tyrosin, &c. The salts in milk consist, according to the average of numerous analyses by Fleischmann, of the following constituents:- . . 28.31 Potash .. . 17'34 Phosphoric acid Chlorine . 16.34 Magnesia . 4.07 Lime . . 27.00 Ferric oxide
Soda . .. IOoo Milk thus is not to be regarded as a definite chemical compound nor even as a mixture of bodies in fixed and invariable proportions. Not only does the milk of different races and breeds of cows vary within comparatively wide limits; the milk of the same animal is subject to extensive fluctuation. The principal causes of variation in the individual are age, period of lactation, nature and amount of food, state of health, and treatment, such as frequency of milking, &c. The following table indicates the range of normal variations: 9000.t0 83.65 Water . Fat . . 2.8o ,, 4.50 Casein and albumin 3'30 ,, 5.55 Sugar . . 3'00 ,, 5.50 Ash . . 0'70 o8o The average quantity of milk yielded by cows is also highly variable, both in individuals and breeds. Milk and Disease.-Although the milk of a perfectly healthy cow may be absolutely sterile, it is difficult to obtain it in that condition. In the report of the joint committee appointed for the purpose by the county boroughs of Bradford, Hull, Leeds, Rotherham and Sheffield in 1908, the following conclusions were drawn
ordinary methods contains bacteria. They are more numerous in the first flow of the milk. (2) There is a great increase in contamination in the milk at each stage before it reaches the customer. This is due to (a) the dirty condition of the cows' udders, (b) the imperfect cleansing of the cans and of the hands of the milkers. The committee recommend:' Ewe's milk is exceedingly variable, especially in its percentage of fat. The above analysis is one of nine by Dr Arthur Voelcker, in which the fat was found to range from about 2 to 121%." (I) The washing of the udder and flanks with soap and water, and similar attention to the hands of the milker. (2) Efficient sterilization of all vessels by steam if possible, or by abundance of boiling water. (3) Rejection of the first draw of the milk from each teat. (4) Avoidance of any work raising dust immediately before or during milking. (5) Removal of the milk of each cow immediately from the shed. (6) Ventilation and cleanliness of the cowsheds.' This provides for the reduction as far as possible of contamination during the milking process itself. As any bacteria present in the milk tend to multiply rapidly on the way to the consumer, it is mainly a question of the time which elapses before consumption. It is, there-fore, further recommended (a) that the milk be rapidly cooled or chilled, as the lower the temperature the less do the bacteria multiply, (b) that contamination during railway transit be avoided by dust-proof locked milk cans. By treating milk at a temperature of 6o C. for one hour, 7o C. for ten minutes, and 950 C. for one minute, tubercle bacilli, if present, will certainly be killed. Cholera and typhoid organisms are less resistant, and are killed more quickly than tubercle bacilli at the above temperatures. Only a single pathogenic species can with-stand the short boiling to which milk is ordinarily treated in domestic management, and this is the anthrax bacillus containing spores. The danger from this source is remote, as the microbe does not form spores within the animal body
body
The lactic acid bacillus, always present in unboiled milk (to which the souring of milk is due), is easily destroyed by heat; but the bacillus mesentericus, often found in it, forms spores, which are not destroyed by ordinary boiling, and germinate when the milk is kept at a moderately warm temperature, producing a brisk fermentation whereby a large volume of gas is liberated. The ,fundamental idea of Soxhlet's method for sterilizing milk is to boil it for forty minutes in small bottles holding just enough for one meal
In short, there is the greatest difficulty in freeing milk on a large scale from germs without at the same time seriously prejudicing its flavour and nutritive value. Since, then, the destruction of the hardy
Since Metchnikoff's introduction (see LONGEVITY) of the use of soured milk for dietetic purposes-the lactic acid bacillus destroying pathogenic bacteria in the intestine-a great impetus has been given to the multiplication of laboratory preparations containing cultures of the bacillus; and in recent
See also the articles ADULTERATION; DAIRY AND DAIRY FARMING; INFANCY; DIETETICS; FOOD and Foot) PRESERVATION; in the last of which the preparation of condensed milk is described. End of Article: MILK (0. Eng. meoluc; from a common Indo-European root, cf. Lat. mulgere, Gr. ?t dXyetv) If you wish, you can link directly to this article.
<a href="http://jcsm.org/StudyCenter/Encyclopedia/MIC_MOL/MILK_0_Eng_meoluc_from_a_commo.html"> MILK (0. Eng. meoluc; from a common Indo-Europe... </a> |
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