In the studies at the Iowa Agricultural Experiment Station on the bacteria in normal and abnormal dairy products, an organism that produces a rather characteristic change has been encountered over a period of years. On comparatively young plates and in litmus milk it commonly develops a sweet, ester-like odor resembling that of the flower of the common May apple (Podophyllum peltatum ). Cultures have been isolated in large numbers from various defective dairy products, especially those held at low temperature, and it appears that the organism is of considerable practical importance. A study of the morphology, cultural characters, biochemical features and growth conditions of many cultures indicates that, although the reactions are not always identical, the cultures constitute but a single species. The variations involve especially colony appearance, action on litmus milk and action on fat. The species was identified as Pseudomonas tragi; it has been investigated from the standpoint of distribution, identification and action on various dairy products, and the results are presented herein.