THE CHEMICAL COMPOSITION OF MILK 27 



absorb as much of the milk-serum as possible. The resulting 

 layer of fat was then scraped from the filter paper, and washed 

 in a beaker with ether to dissolve the fat. This was then fil- 

 tered, and the residue smeared on coverslips, stained with 

 carbolized hematoxylin and then with eosin. A few fibrin 

 threads were demonstrated in this manner. 



"Another plan was to filter the milk through a hardened 

 filter. This filter resembles parchment and is designed to 

 stand suction. Milk filters very slowly by this means, and there 

 can be little doubt that any fibrin threads are retained. The 

 resultant filtrate was scraped into a beaker, washed with ether, 

 filtered again, and the filtrate smeared on coverslips, and 

 stained in the usual way. This method worked very satisfac- 

 torily in most instances, and the fibrin threads were easily 

 demonstrated. This work should confirm Babcock's fibrin 

 theory." 



Milk-sugar 



Cow's milk normally contains between 4 and 6 per cent of 

 milk-sugar or lactose in solution in the milk-serum. Its chemical 

 composition is the same as cane-sugar, Ci 2 H 22 0ii + H 2 0, but 

 it does not readily dissolve in water and therefore is not as 

 sweet to the taste as is cane-sugar; 1 part of milk-sugar will 

 dissolve in 6 parts of cold water or 2-J parts of boiling water. 

 Its specific gravity is 1.525. It is of considerable commercial 

 value and is much used in the preparation of modified milk for 

 infant feeding. Lactose is readily broken up by the action of 

 lactic acid bacteria, one molecule of the sugar forming four 

 molecules of lactic acid. This fermentation normally begins 

 soon after the milk is drawn from the cow and, unless it is 

 checked, goes on rapidly until enough sugar has been changed 

 to acid to coagulate the milk. As the lactic acid accumulates 

 in the milk, it reacts upon the activity of the bacteria, which 

 practically cease their action when the acidity has reached 



