The importance of cow's milk in the dietary of the well and the sick alike, and its indispensability as an article of food in the nourishment of a great group in our infant population tend to keep alive a wide-spread interest in the quality and purity of the available supply.
The significance of bacteria in milk, their influence in modifying its keeping properties, their possible danger as sources of infection—all of these facts have become a part of the common store of knowledge. Information concerning them has been spread broadcast, in magazines and daily newspapers. The problem of other structural elements in milk has not reached the public eye to the same extent; indeed, it has scarcely passed beyond the stage of scientific inquiry.
Many of the secretions of the body contain cells discharged from the tissues, and these cells in general are of two kinds: (a) epithelial cells discharged