As fermented milks of diverse sorts have come into use not merely as foods but also as products of reputed therapeutic and prophylactic value, physicians should have a clear understanding of their manufacture and chemical nature. In many of the larger cities, special fermented milk preparations can be obtained under various trade names which supplant the more familiar terms buttermilk, kefir, koumiss and yoghurt. The latter types, however, include the most important varieties that are well known, so that an understanding of their origin ought to give a fairly clear appreciation of the possibilities in this field.1
Almost every one who has had any acquaintance with farm life or dairy products knows the process leading to the production of buttermilk as a by-product in butter making. It is not so generally appreciated, however, that in recent years much of the so-called buttermilk sold for human use in this country