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A complete review of the literature on the extensive subject of sporulation in bacteria will not be undertaken here. The reader is referred to the exhaustive review of Knaysi (1948). The literature dealing with spore formation in bacteria is generally divided into three different categories, corresponding to three major interpretations of the process. The first of these interpretations, originated by Cohn (1876) for Bacillus subtilis, and by Koch (1876) for Bacillus anthracis, places the origin of the spore in a single granule. This granule makes its appearance as spore formation commences and rapidly increases in size and refringence. The second interpretation originated with Zopf (1883), who explained spore formation in Bacillu-s tumescens as an aggregation of several refractile granules. A process which must be placed in this category was described by Schaudinn in 1902 for the disporic organism, Bacillus biitschlii, and is of considerable importance because of the biologic significance attached to it by the author. The disappearance of a cross wall and the rearrangement of chromatinic granules into an axial spiral preceding their aggregation were interpreted as a primitive copulation of incompletely separated daughter cells. Dobell (1908) described a process in Bacillus flexilis identical to that proposed by Schaudinn. Later, presenting an altered concept (1909, 1911), Dobell challenged Schaudinn's interpretation of sexuality on the basis that a similar situation, with the formation of two spores, can arise in the monosporic organism, Bacillus spyrogyra, and merely represents an abortive cell division, not a sexual process. The third interpretation supposes the formation of spores by progressive condensation of the protoplasm. The gradual accumulation of "volume" of the "prespore" area suggested by the first two concepts differs from that suggested here in that spore formation is heralded by the sudden appearance of an evenly opaque spore primordium. This is denser than the cytoplasm and slightly larger than the finished spore. The contents of this area gradually increase in density and refringence, and a spore wall forms. Preisz (1904), who described this process in great detail for Bacillus anthracis and Clostridium tetani, observed a round or elongated nucleus within the spore primordium which disappears during maturation of the spore. Advocates of sporulation by condensation of the protoplasm are many, and their names need not be mentioned here.

THE NUCLEAR CYTOLOGY OF SPORULATION IN BACILLUS MEGATERIUM