COMPOSITION OF MILK. 347 



of the calf, while a 5 per cent. NaCl solution of the seeds of Withania coagulans coagulates milk 

 in an alkaline medium.] 



Boiling (by killing all the lower organisms), sodium bicarbonate (tuVcOj ammonia, salicylic 

 acid (r?nnr)> glycerine, and ethereal oil of mustard prevent the spontaneous coagulation. Fresh 

 milk makes tincture of guaiacum blue, but boiled milk does not do so. When milk is exposed 

 to the air for a long time, it gives off C0 2 and absorbs ; the fats are increased (? owing to the 

 development of fungi in the milk), and so are the alcoholic and ethereal extracts, from the de- 

 composition of the casein. According to Schmidt-Mulheim, some of the casein becomes con- 

 verted into peptone, but this occurs only in unboiled milk. 



Composition. 100 parts of milk contain 



Human milk contains less albumin, which is more soluble than the albumin in the milk of 

 animals. 



Colostrum contains much serum-albumin, and very little casein, while all the other substances, 

 and especially the fats, are more abundant. 



Gases. Pfliiger and Setschenow found in 100 vols, of milk 5*01 to 7 '60 C0 2 ; 0-09 to 0*32 O ; 

 # 70 to 1*41 N, according to volume. Only part of the C0 2 is expelled by phosphoric acid. 



Salts. The potash salts (as in blood and muscle) are more abundant than the soda com- 

 pounds, while there is a considerable amount of calcium phosphate, which is necessary for form- 

 ing the bones of the infant. Wildenstein found in 100 parts of the ash of human milk sodium 

 chloride, 1073 ; potassium chloride, 26"33 ; potash, 21'44 ; lime, 18*78; magnesia, 0*87; 

 phosphoric acid, 19 ; ferric phosphate, 0*21 ; sulphuric acid, 2*64 ; silica, traces. The amount 

 of salts present is affected by the salts of the food. 



Conditions Influencing the Composition. The oftener the breasts are emptied, the richer the 

 milk becomes in casein. The last milk obtained at any time is always richer in butter, as it 

 comes from the most distant part of the gland viz., the acini. Some substances are dimin- 

 ished and others increased in amount, according to the time after delivery. The following are 

 increased: Until the 2nd month after delivery, casein and fat ; until the 5th month, the salts 

 (which diminish progressively from this time onwards) ; from the 8th to the 10th month, the 

 sugar. The following are diminished: From 10th to 24th month, casein ; from 5th to 6th 

 and 10th to 11th month, fat ; during 1st month, the sugar ; from the 5th month, the salts. 



The greater the amount of milk that is secreted (woman), the more casein and sugar, and the 

 less butter it contains. The milk of a primipara is less watery. Rich feeding, especially pro- 

 teids (small amount of vegetable food), increases the amount of milk and the casein, sugar, and 

 fat in it ; a large amount of carbohydrates (not fats) increases the amount of sugar. 



[Modifying Conditions. That cow's milk is influenced by the pasture and food is well known. 

 Turnip as food gives a peculiar odour, taste, and flavour to milk, and so do the fragrant grasses. 

 The mental state of the nurse influences the quantity and quality of the milk. Jaborandi is 

 the nearest approach to a galactagogue, but its action is temporary. Atropin is a true anti- 

 galactagogue. The composition of the milk may be affected by using fatty food, by the use of 

 salts, and above all by the diet (Dolan).'] 



[Milk may be a vehicle for communicating disease by direct contamination, from the 

 water used for adulterating it or cleansing the vessels in which it is kept ; by the milk absorb- 

 ing deleterious gases ; by the secretion being altered in diseased animals.] Milk ought not to 

 be kept in zinc vessels, owing to the formation of zinc lactate. 



Substitutes. If other than human milk has to be used, ass's milk most closely resembles 

 human milk. Cow's milk is best when it contains plenty of fatty matters it must be diluted 

 with its own volume of water at first, and a little milk-sugar added. The casein of cow's milk 

 differs qualitatively from that of human milk ; its coagulated flocculi or curd are much coarser 

 than the fine curd of human milk, and they are only f dissolved by the digestive juices, while 

 human milk is completely dissolved. Cow's milk when boiled is less digestible than un- 

 boiled. 



Tests for Milk. The amount of cream is estimated by placing the milk for twenty-four 

 hours in a tall cylindrical glass graduated into a hundred parts or creamometer ; the cream 

 collects on the surface, and ought to form from 10 to 24 vols, per cent. [The cream is gene- 

 rally about t^.] The specific gravity (fresh cow's milk, 1029 to 1034 ; when creamed, 1032 

 to 1040) is estimated with the lactometer at 15 C. The sugar is estimated by titration with 

 Fehling's solution ( 150, II.), but in this case 1 cubic centimetre of the solution corresponds 

 to 0*0067 grm. of milk-sugar ; or its amount may be estimated with the polariscopic apparatus 



