MILK 19 
may undergo different varieties of fermentation when 
acted on by microérganisms. Certain bacteria split up 
lactose into lactic acid and certain by-products (carbon 
dioxide, hydrogen, formic acid, butyric acid, etc.). These 
organisms are the cause of the common “souring” and 
curdling of milk. The bacteria of the coli-aerogenes 
group ferment lactose and form acids and gases (lactic, 
acetic, and succinic acids, carbon dioxide, carburetted 
hydrogen, oxygen, and nitrogen). 
Under normal conditions, lactose is found only in 
the milk. If milk is retained in the udder from any 
cause, as incomplete milking, omission of milking, udder 
disease, etc., then lactose appears in the urine. When a 
secreting udder is completely extirpated, glucose is tem- 
porarily present in excess in the blood and appears in 
the urine, while lactose appears in the urine if the udder 
tissue is not completely removed. These latter facts are 
taken to indicate that milk sugar is formed in the udder 
from the glucose carried to it by the blood. 
Salis—The salts of milk, which are in solution, are 
very largely inorganic. Calcium, potassium, and sodium, 
together with small quantities of magnesia and oxide 
of iron, are present in combination with phosphoric acid, 
sulphuric acid, chlorine, and carbonic acid. A small por- 
tion of the basic substances is in combination with citric 
acid and probably with other organic acids. 
W ater —The water of milk is derived from the blood. 
The milk constituents, except the water, are referred 
to as the milk solids, total solids, or dry matter. The 
casein, albumin, globulin, lactose, and salts are desig- 
nated as solids not fat. 
Variations in Composition.— While normal milk always 
contains the same chemical constituents, the proportions 
