juiy 31. 1916 Life Cycles of the Bacteria 681 



Type F comprises all small rodlike cells of different form, straight or 

 curved, about 0.3 to 0.5/x broad, 0.75 to 1.5M, or more, long. When not 

 forming spores, they may be labeled Fa; otherwise F/3. Cells of the 

 Fa type occasionally look very much like B. radiobacter and related 

 species. In cases where great difficulties were encountered in getting a 

 pure culture of B. azotobacter, this type of growth probably has repeatedly 

 displayed an unwelcome activity. When developing from the symplastic 

 stage, type F/3 shows different and somewhat unusual-looking inter- 

 mediate forms (fig. 15 of PI. C). For making a spore-bearing rod of the 

 " Plectridium " type, a body splits off from the symplasm, showing a 

 comparatively large "head" and a very small pointed "tail." When 

 the tendency prevails, however, to form a "Clostridium", the well- 

 stained regenerative unit is located inside a pale sheath with pointed ends 

 and in growing stretches until the albuminous substance is equally 

 distributed inside the cell wall. Later, a part of the protoplasm once 

 more concentrates, developing the spore. Spore -free, as well as spore- 

 bearing, thin threads can directly, without passing through type D, 

 change into the large type L. (See below.) On the other hand, they can 

 also originate directly from this type (fig. 20 of PI. D). In the latter case 

 they sometimes resemble type G, from which they differ, however, by 

 their spore formation and their genesis. 



Type G shows, when treated with aqueous fuchsin, unevenly stained, 

 frequently branched threads looking very much like Actinomyces. 

 It is, however, as indicated in text figure 1 and shown in figure 16 (PI. C), 

 merely an intermediate step between types D and E which may be 

 dispensed with. The small cells of type E are kept together by un- 

 stainable slime. Boiling water dissolves this slime within two minutes. 

 A preparate treated accordingly with boiling aqueous fuchsin shows 

 merely t)^pe E or some threads just dissolving (fig. 17 of PI. C). 



Type H acts as the counterpart of type C. There the larger, here the 

 smaller cells are undergoing a granular decomposition leading to type D. 

 However, rods, as well as spores, show a very unusual appearance in 

 this case. They become entirely unstainable by aqueous dyes, but 

 remain clearly visible even with a wide-open condenser, owing to the 

 very bright luster of their granular content (fig. 18 of PI. C). 



Type I represents the globular, oval, or rodlike "regenerative" bodies 

 which have been studied by Prazmowski (18). Here, again, an added 

 a or 13, respectively, may indicate their more or less resistant character 

 (thin or thick cell wall) . la usually originates from types A and B (fig. 

 5 of PI. A) or from type C (fig. 7 of Pi. B). 10, on the other hand, in 

 most cases is an offspring from the symplastic stage D (fig. 13 of Pi. C). 

 Irregularly shaped type I, which is quite frequent with the other bacteria i 

 has been observed only occasionally in cultures of Azotobacter (fig. 16 

 of PI. C). The regenerative bodies either produce, by germinating or by 

 stretching, cells of type A, B, or L, or they convert themselves entirely into 



