SECRETION :'.45 



proteins unites with the liberated calcium phosphate to form 

 the insoluble curd. Casein is insoluble in water, alcohol, 

 ether, and dilute acids, but soluble in strong acids and in 

 alkalies. 



Lactalbumin is coagulated by heat and precipitated by 

 tannin and saturated solutions of sodium and magnesium 

 sulphates. It contains carbon, hydrogen, oxygen, nitrogen, 

 and sulphur, but no phosphorus. 



(d) Inorganic Salts are present in the form of chlorides 

 of sodium and potassium, mono- and dipotassium phos- 

 phates, dimagnesium phosphate, di- and tricalcium phos- 

 phates, calcium and magnesium citrates. All the salts 

 are present in solution except tricalcium phosphate, which 

 is suspended in finely divided form. It is to be noted that 

 some of the inorganic elements are combined with citric acid. 

 It may be noted that an increase in the amount of inorganic 

 salts raises the specific gravity. 



(e) Other Constituents. — In addition to those substances 

 already mentioned, milk contains lecithin, cholesterol, pro- 

 teolytic enzymes, carbon dioxide, oxygen and other gases, 

 especially when the milk is fresh drawn, not to mention 

 various kinds of foreign matter including bacteria. The 

 amount of dirt and bacteria depends on the care with which 

 milk is handled. 



245. Secretion. — Milk is secreted in certain glands espe- 

 cially adapted for the purpose, and evidence points to the 

 fact that the various components of this fluid are elaborated 

 in these gland cells only and not merely filtered from the 

 blood plasma. Lactose, for example, is not found in the 

 blood stream, but must be manufactured, probably from 

 dextrose, in the milk glands. Milk fat and casein are not 

 found in any other part of the body. 



The influence of breed of cow on the quality of milk 

 secretion is of much greater importance than that of food. 

 The Jersey, for example, produces large globules of milk 

 fat, which causes cream to rise rapidly and in considerable 

 quantities. The Holstein produces small globules of milk 

 fat and not so great a total quantity. Modifying the food 

 has very little influence on the composition of milk. The 



