The appliances for the souring of milk on the domestic scale require some consideration. We propose to describe the principal forms of apparatus which have been put on the market for the purpose, and then to give such suggestions as may assist the ingenious in making apparatus for themselves. Those who wish for information on the subject of larger apparatus will find it in the following chapter. [Illustration: FIG. 41—Photograph of Agar Culture, inoculated with a lactic powder offered to consumers under a fancy name. Working on the assumption that the presence of lactic bacteria is inimical to the growth of septic organisms, this preparation has been placed on the market. The plate shows, however an abundance of colonies of foreign organisms—sporogenous bacilli, _Staphylococcus pyogenes albus_, and _Staphylococcus pyogenes aureus_. These organisms are shown in the appended photo-micrographs, and constitute impurities in the preparation.] [Illustration: Spore forming bacillus] [Illustration: _Staphylococcus pyogenes albus_] [Illustration: FIG. 42—Photograph of Test Tubes of Sterile Milk, inoculated with a tablet preparation said to contain pure cultures. The darker liquefied portion of the tube-contents is due to digestion of the curd by proteolytic bacteria, thus indicating impure culture. Pure cultures of lactic acid bacteria coagulate the milk uniformly, but do not produce any subsequent change in the appearance of the culture, even after several months.] [Illustration: FIG. 43—Photograph of Test Tubes of Sterile Milk, each tube having been inoculated with a tablet of a preparation said to contain pure cultures. Here, again, there is evident peptonisation of the curd, thus indicating infection by proteolytic ferments. Cultures from these tubes demonstrated the presence of a foreign organism. Microscopical examination failed to disclose the presence of _Bacillus Bulgaricus_.] [Illustration: FIG. 44—Photograph of Test Tubes of Sterile Milk, inoculated with a tablet of "Lactobacilline." In contra-distinction to those shown in Figs. 42 and 43, these tubes exhibit homogeneous curdling of the milk without any subsequent digestion or peptonisation of the coagulum. This is indicative of the purity of the culture.]