2IO ORGANIC AGRICULTURAL CHEMISTRY 



easily soluble in water and crystallizes in large crystals. It 

 does not taste quite as sweet as cane sugar, but is more easily 

 digested ; at least human beings, and probably all mammals, 

 are able to digest it before any other carbohydrate. It is the 

 sole carbohydrate food so long as the animal lives upon milk 

 alone. It reduces Fehling's solution and may be tested for or 

 determined quantitatively by means of this reagent. 



An important property of milk sugar is that certain bacteria, 

 viz. lactic acid bacteria, ferment it with the production of lac- 

 tic acid. The lactic acid so produced is the cause of what is 

 termed the souring of milk and is also connected with the sepa- 

 ration of the protein casein. Milk sugar is obtained from milk 

 in considerable quantities for use as an infant food and the 

 sugar left in whey is used without separation for the commer- 

 cial preparation of lactic acid. 



Fats. — The fat constituents of milk are contained largely 

 in the cream, which may be separated from it, and in butter 

 the most important milk product. As has been previously ex- 

 plained, fats are esters of glycerol and organic acids. With 

 two exceptions, the acids present as esters in milk fat belong 

 to the monobasic saturated acids of the acetic acid series. The 

 exceptions are oleic acid, the eighteen-carbon acid of the ethy- 

 lene unsaturated series, and a dihydroxy derivative of stearic 

 acid, the eighteen-carbon saturated acid. 



The acids found in milk fat, as glycerol esters, are the follow- 

 ing in the order of their amounts present as given by Browne : 



Palmitic acid C15H31COOH 



Oleic acid C17H33COOH 



Myristic acid C13H27COOH 



Butyric acid C3H7COOH 



Laurie acid C11H23COOH 



Caproic acid C5H11COOH 



Stearic acid C17H35COOH 



Dioxystearic acid Ci7H33(OH)2COOH' 



Caprylic acid C7H15COOH 



Capric acid CgHxgCOOH 



