316 
In the preparation of this communication we have drawn freely | 
from the writings of numerous authors on the subjects herein con- 
sidered. In every instance the attempt has been made to give due i| 
credit to all concerned and no special credit is claimed for any orig- : 
inality in the treatment of any of the subjects herein presented. 
Free use has been made of many treatises and works on the subject ^ 
of milk and milk analysis and of many original articles and mono- i 
graphs treating of the composition of milk, the rennin coagulation, i| 
the milk ferments, the use of coloring matters and preservatives and {i 
their possible injurious effects. For all of these due acknowledg- | 
ment is hereby made. To Conn, “Agricultural Bacteriology,” Phila- ti 
delphia, 1901, we are especially indebted for much on the subject of | 
the abnormal fermentations of milk. To Leach, “Food Inspection j 
and Analysis,” New York, 1907, and to Van Slyke, “ Modern Methods ij 
of Testing Milk and Milk Products,” New York and London, 1907, || 
for methods pertaining to milk analysis, and for valuable data on the 
composition of milk and milk adulteration. To the health office of 
the District of Columbia we are indebted for much assistance during 
the progress of the work, and to Prof. Victor C. Vaughan, of the 
University of Michigan, for private information relative to recent 
progress in the field of milk poisons. 
PART I.— THE COMPOSITION AND GENERAL CHARACTERISTICS OF 
MILK. 
Milk is the specific secretion of the mammary glands.® The milk 
of a number of animals has been and is still very extensively used ; 
as food by man. The milk of different animals shows a general : 
agreement in physical properties and composition, containing essen- 
tially the same ingredients but exhibiting differences in the amounts 
of the several constituents. Of all the different kinds of milk, that 
of the cow is the most universally used, and in what follows, unless * 
expressly stated to the contrary, it will be understood that cow’s milk 
is meant whenever the term “ milk ” is employed. | 
In the perfectly fresh state, milk is a yellowish-white, opaque fluid. | 
When allowed to stand undisturbed for some time it separates into 
two distinct layers. The upper, lighter layer, occupying a smaller 
volume than the lower, heavier layer, is what is called “ cream,” and 
consists largely of globules of fat. The lower, heavier layer, white 
® Ordinarily milk is secreted by the female mammal only, and only after par- 
turition. In some instances, however, the mammae of newborn children, males 
as well as females, also secrete small amounts of a milk-like fluid known as 
witch’s milk; and still more rarely milk is said to have been secreted by the 
mammary glands of the adult human male. Fluids resembling milk are also 
formed in certain pathological conditions. All of these instances are, however, 
more or less rare and warrant no further consideration in this connection. Milk- 
like secretions of vegetable origin are also not considered in this communication. 
