Bienstock has shown that the growth of _Bac. putrificus_ is inhibited by the action of _Bact. coli commune_, which is capable of setting up a slight lactic acid fermentation. _Bact. coli commune_, however, gives rise to substances of an injurious character, and, although present very abundantly in the intestinal tract, it may by reduced almost entirely by the active growth of lactic acid bacteria. This fact is of great value to the cheese-maker, since by the addition of a lactic acid culture (starter) to milk before renneting, gas-producing bacteria such as _Bact. coli_ may be checked in growth. Since the ordinary lactic acid bacteria such as _Streptococcus lacticus_, _Bac. lactis acidi_, and others, are incapable of growth at blood temperature, it appeared necessary to procure cultures of lactic bacteria able to grow at temperatures of 100° F. to 112° F. Such an organism was found in Bulgarian soured milk (yoghourt), and was considered pre-eminently adapted to this purpose. As has been shown in the preceding paragraphs, this organism is merely one of a large group of bacteria found distributed in the intestinal canal of many domestic animals, in manure, and in ordinary market milk. It is then not surprising that the introduction into the intestinal tract of bacteria of the type _Bulgaricus_ in the form of tabloids has not met with any decided success. Although it was considered to be merely necessary to introduce the desired type of organism into the body, and the amount of lactic acid taken into the system by the administration of soured milks was looked upon as of secondary importance, yet, it would seem, in the light of recent investigations, that benefits derived from a soured milk regimen are attributable in part to a chemical as well as a purely bacterial action. This receives support from the fact that soured milk beverages prepared by the use of ordinary lactic bacteria, distinct from those of the _Bulgaricus_ type, often exert a beneficial influence upon human beings even although the organisms responsible for the fermentation are incapable of growth at blood temperature. It may be mentioned in conclusion that cultures prepared by the use of organisms of the type _Streptococcus lacticus_ combined with _Bac. bulgaricus_ possess a more agreeable flavour and aroma than those prepared from a pure culture of _Bulgaricus_ alone. [Illustration: FIG. 35—_Bacillus bulgaricus_, showing the cultures in English cow's milk. (Magnified 450 diams.)] [Illustration: FIG. 36—Photo-micrograph of pure culture of _Bacillus bulgaricus_. The administration of cultures of this organism is indicated in all cases of intestinal ailments, caused by the excessive growth of proteolytic bacteria, and consequent putrefaction of foods in the alimentary tract. By the formation of large quantities of lactic acid, a state of asepsis is ensured, which is particularly valuable in cases of operations on the abdomen and intestines.]