_Yoghourt and Soured Milk._—Yoghourt is another fermented milk, and is related to the matzoon of Armenia, the gioddu of Sardinia, and the leben of Egypt. After a preceding boiling and reduction of the volume of the milk, inoculation of the mass is made by the addition of a small quantity of old culture, and it is then allowed to sour at a comparatively high temperature. A moderately compact, jelly-like coagulum is thus formed, while keffir and koumiss possess a liquid consistency. The fermentation necessary for the two latter products only proceeds, too, at a much lower temperature, at which yeasts play an important part. According to Guerbet, yoghourt incubated for ten hours at 113° F. contained 0.34 per cent. lactic acid and 0.012 per cent. alcohol. Luerssen and Kühn[70] came to the conclusion that yoghourt contained chiefly a mixture of _Bacillus bulgaricus_, diplostreptococci, and a "granule" bacillus, so called on account of its granulated appearance after treatment with methylene blue. According to these authors, the first two organisms were found in each of eight samples of maya (young yoghourt) and of yoghourt itself, but the occurrence of the "granule" bacillus in plate cultures was by no means regular. In addition, yeasts were found in almost every sample examined, but were regarded more as accidental infections rather than as essential to the formation of a typical product. The combined action of the three organisms already mentioned gave rise to a product closely resembling normal yoghourt. Piorkowski[71] subjected Bulgarian maya to examination and associated himself with Metchnikoff[72] in finding three species, a streptococcus, a diplococcus, and a specific organism to which he gave the name _Yoghourt bacillus_. Similar results were also obtained by Grigoroff.[73] Piorkowski's _Yoghourt bacillus_ is similar in form to _Bacillus subtilis_, but does not sporulate, nor does it liquefy gelatine. Young individuals are stained by Gram's method; older individuals are, however, Gram negative. The optimum temperature is 112° F. Kuntze attempted to isolate the organisms mentioned by Luerssen and Kühn, and by plate culture procured growth of a spore-forming bacillus similar to Weigmann's _Bacillus matzoon_. To this organism is attributed the power to impart a specific taste to the matzoon, but as growth is comparatively slow, it can only be of significance in determining the quality of the curd and cheese prepared from this product. Cultures were also obtained which resembled in general character those of the organism described by Luerssen and Kühn as _Bacillus bulgaricus_ and named by Kuntze _Bacterium W_. Granule formation was transient in this culture, and the organisms eventually became inactive. Further analysis of maya gave cultures of the "granule" bacillus, but these passed over from the type forming irregular colonies (see Figs. 14, 15, 16) to that producing smooth colonies. Further, although the granule formation persists