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siderecl. In every instance the attempt has been made to give due 
credit to all concerned and no special credit is claimed for any orig- 
inality in the treatment of airy 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- 
graphs treating of the composition of milk, the rennin coagulation, 
the milk ferments, the use of coloring matters and preservatives and 
their possible injurious effects. For all of these due acknowledg- 
ment is hereby made. To Conn, “ Agricultural Bacteriology/ ’ 
Philadelphia, 1901, we are especially indebted for much on the sub- 
ject of the abnormal fermentations of milk. To Leach, “Food 
Inspection and Analysis/’ New York, 1907, and to Van Slyke, 
“Modern Methods of Testing Milk and Milk Products/’ New York 
and London, 1907, for methods pertaining to milk analysis, and for 
valuable data on the coiriposition 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. 
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 gen- 
eral agreement in physical properties and composition, containing 
essentially 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 fol- 
lows, 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 sepa- 
rates 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 or bluish white in color, is when separated known as “skim milk.” 
On account of changes due to the growth and action of micro-organ- 
a Ordinarily milk is secreted by the female mammal only, and only after parturi- 
tion. 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 patho- 
logical 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. 
