The concept of the « struggle for existence » has been applied to microbial interrelationships in nature in a manner comparable to the effects assigned by Darwin to higher forms of life. It has also been suggested that the ability of a microbe to produce an antibiotic substance enables it to survive Giom. in competition for space and for nutrients with other microbes. Such assumptions ppear to be totally unjustified on the basis of existing knowledge. Before we proceed with a discussion of the formation and activities of antibiotics under natural conditions, we must consider certain fundamental aspects of the problem of antibiotic production under controlled laboratory or factory conditions... All the discussion of a "struggle for existence" in which antibiotics are supposed to play a part, is merely a figment of the imagination, and an appeal to the melodramatic rather than the factual.