reserve material and protected by a more or less resistant membrane. Gonidia and regenerative bodies participate actively in the process of multiplication, whereas the other reproductive organs are in the first place resting forms. Gonidia, regenerative bodies, and probably microcysts are produced by all bacteria, while arthrospores, exo-and endospores are less common; though there are indications that they will be discovered in many more cases, as soon as these problems are more thoroughly investigated (1921, p. 162). All bacteria live, in vivo as well as in vitro, alternately in an organized and in an amorphous stage. By the partial or complete dissolution of the vegetative and reproductive cells, a plasmatic mass, the symplasm, is formed, which, after a period of rest, according to circumstances may transform itself into new cells of the same or of a more or less modified character The formation of the bacterial symplasm proceeds always in two phases: First, the cells agglomerate to smaller or larger clumps; second, a more or less complete dissolution of the cells takes place, resulting in a crumbly or slimy mass The reconstruction of new cells from the bacterial symplasm follows various lines according to the internal as well as the external conditions (quality of the symplasm, environment, and technique). At first always regenerative units become visible, which either grow up separately to new cells, or of which several may agglomerate and surround themselves with a uniting membrane, thus forming at once full-grown cells. (1921, p. 195). He also describes another process as conjunction, where two or more cells combine without previous disintegration. Lohnis is careful to point out that "by discussing the life cycles of bacteria we do not intend to revive any of those unclear theories concerning bacterial polymorphism or pleomorphism. The development of bacteria is characterized not by the irregular occurrence of more or less abnormal forms but by the regular occurrence of many different forms and stages of growth connected with each other by constant relations" (1916, p. 677). But the diagram which he presents to show these constant relations, with its numerous arrows connecting each type with many others, and with double points indicating their reversibility, leaves one without any clear notion of regularity, but rather with the idea, in vogue in Naegeli's day, that any bacterial type may develop in a haphazard way from any other. Indeed, from neither text nor illustrations can one gain any exact impression of the sequence of events in the life cycle he postulates. Mellon, in a long series of papers extending over ten years, has described morphologic variations in diphtheroid bacteria, typhoid and colon bacilli, and fusiform organisms; many of his papers deal with 35, 36, 37, 38 Minot, C. S
