Milk, as sold in most large cities, is often adulterated to a great extent, but most frequently with water. Not unfrequently, too, a part of the cream is first taken off, and water afterwards added; in which case the use of burnt sugar is very common for coloring the milk, the blueness of which would otherwise lead to detection. The adulteration of pure milk from the healthy cow by water, though dishonest, and objectionable in the highest degree, is far less iniquitous in its consequences than the nefarious traffic in “swill-milk,” or milk produced from cows fed entirely on “still-slops,” from which they soon become diseased, after which the milk contains a subtle poison, which is as difficult of detection by any known process of chemistry as the miasma of an atmosphere tainted with yellow fever or the cholera. The simple fact is sufficiently palpable, that no pure and healthy milk can be produced by an unhealthy and diseased animal; and that no animal can long remain healthy that is fed on an unnatural food, and treated in the manner too common around the distilleries of many large cities. [Illustration: Fig. 71.] It is evident, from the well-known influence which “still-slops” and other exceedingly succulent food have in increasing the amount of water in the milk, that adulteration may be effected by means of the food, as well as by addition of water to the milk itself. It is evident, too, on a moment’s reflection, that the specific gravity of pure milk must vary exceedingly, as it comes from different cows, or from the same cow at different times. This variation reached to the extent of twenty-three degrees in the milk of forty-two different cows, or from one thousand and eight to one thousand and thirty-one; but so great a variation is very rare, and not to be expected.