IN an interesting article on the symbiosis between myxobacteria and nitrifying bacteria, Imsenecki1 describes an observation which he made during his studies on the biology of myxobacteria, when he was able to isolate from a culture of Nitrosomonas, grown in its elective medium, a heterotrophic organism which he has named Sorangium symbioticum. He postulates a symbiotic existence for these two organisms, suggesting that the development of the nitrifying bacteria precedes that of the myxobacteria, and that these chemotrophic nitriflers synthesize the organic material needed for the heterotrophic organisms, afterwards making this available by the autolysis of the Nitrosomonas cells. Unfortunately no quantitative data have been published1.