PHYSIOLOGY OF MILK SECRETION. 203 



SOLUBLE FATS. 



Butyrin 4.67 Butyric acid 3.49 



Caproin 3 . 02 Caproic acid 2 . 40 



Caprylic acid and 



Caprylin and Rutin 10 Rutic acid 80 



7.79 6.69 



The insoluble solids constitute a little more than 92 per cent, of the total 

 fat, are stable and suffer little from the organized ferments. They are taste- 

 less and nearly neutral. They are composed of glycerol united with fatty 

 acids. The peculiarity of these fats lies in the proportion of the different ones 

 present. The presence of a greater proportion of stearin raises the melt- 

 ing point, while a high proportion of olein lowers it. 



The proportion of these fats is fairly constant, but in the case of feed- 

 ing cotton seed meal to cattle, the melting point of butter is raised and 

 would seem to indicate that the per cent, of stearin was increased. No 

 analyses are available to determine whether this is the case or not. 



The volatile fats constitute less than eight per cent, of the total fats 

 in milk, but they are of great importance, as they impart the taste and 

 odor and give the peculiar animal characteristics. They are probably more 

 easily affected than any other constituent of milk. 



The casein is the chief proteid constituent of milk. It is insoluble in 

 water and exists in milk in a semi-colloidal condition. It differs from other 

 proteids in that it is coagulated by rennet and dilute acid, but not by heat. 



Albumen is the soluble proteid of milk, and is similar to blood albumen. 

 It is coagulated by heat when subjected to a temperature of 175 to 180 

 degrees Fahr. 



Lactose or milk sugar is a carbohydrate peculiar to milk, as it is found 

 nowhere else. It differs from cane sugar in that it is less soluble in water, 

 has less specific gravity, only a slightly sweetish taste, does not readily un- 

 dergo alcoholic fermentation, but is easily broken up by lactic acid form- 

 ing bacteria. 



Babcock and Russell have demonstrated that milk also contains an or- 

 ganized enzyme, which will cause slow changes upon standing. Their studies 

 have not been continued for a sufficient length of time to give it a full 

 description. 



The organic acid is citric acid, and probably exists most often in com- 

 bination with calcium and potassium. 



The ash or inorganic constituents of milk represent less than one per 

 cent. They exist in compounds of sodium, magnesium, calcium, iron and 

 phosphorus. 



These salts exist in soluble and insoluble states. The soluble salts 

 are sodium chloride and potassium citrate, and the insoluble phosphates 

 of magnesium, calcium, potassium and iron. 



It is also of interest to note in this connection that the inorganic matter 

 in milk exists in the same relative proportions as in the new born. The 



