IN a former article1 the nature, preparation, and uses of soured milk were dealt with. It was pointed out that the consumption of sour milk is wide-spread in the East, that in all the sour milks a peculiar micro-organism is present, with artificial cultures of which it is possible to prepare soured milk in imitation of the natural product, and that soured milk tends to lessen intestinal putrefaction and seems to be beneficial in many complaints. The micro-organism (Bacillus bulgaricus) present in all the natural sour milks is one possessing distinct and special characteristics, though exhibiting marked variation or “pleomorphism,”and Makrinoff,2 who has critically studied the question, believes that all the varieties which have been described are referable to one species. Two more or less distinct races seem to exist, namely, one that produces a somewhat viscous product, another that does not, and for the preparation of soured milk the latter is to be preferred as yielding a more palatable product. The morphological and staining characters of the Bacillus bulgaricus are so distinctive that a microscopical examination, combined with the Gram staining process, of the soured milk, enables us to judge to what extent the B. bulgaricus has developed, and whether there is contamination with other organisms (Figs, 1 and 2).