422 



Cytological observations on Bact. coli 



Fig. 5 (from a preparation mounted in Canada balsam). 

 A typical two-cell bacterium with four chromatinic 

 bodies, three of which are dumbbell-shaped and must 

 be considered as having been in a state of rest at the 

 time of fixation. 



In fig. 6 (mounted as in fig. 5) a represents a stage com- 

 parable to c in fig. 2, while b is another two-cell bac- 

 terium with four dumbbell-shaped chromatinic bodies. 



Fig. 7. In the large bacterium below and to the right of 

 the centre the first dumbbell body from the left as 

 well as the fourth are at rest while the greater width 

 and asymmetrical shape of the two middle ones again 

 suggest a process of division (reduplication). 



Fig. 8. All four chromatinic structures in the large 

 bacterium are preparing to divide. 



Fig. 9. Separation of daughter chromatinic bodies has 

 begun in the two middle ones of the four chromatinic 

 structures in the large bacterium ; less densely stained 

 than the chromatinic bodies of fig. 7, they correspond 

 to the stage of fig. 3, i.e. that of impending separation 

 of the products of a recent longitudinal division. 

 A faintly stained cell boundary traverses the gap 

 between the two pairs of chromatinic configurations. 

 The same type of two-cell rod is also found at e in 

 fig. 2 and at h in fig. 1. At a a filamentous structure 

 connects recently separated, complex chromatinic 

 structures. A slender rod with a long core of chroma- 

 tinic matter is seen in the right-hand top corner; 

 others are visible in figs. 1 and 2. The development of 

 these forms is explained in the text. 



Figs. 10-12. From a culture of Proteus vulgaris of 1 hr. 

 incubation, prepared from the coccoid elements with 

 poorly differentiated chromatinic structures, that form 

 the first belt of confluent growth inside the zone of 

 swarming filaments at the periphery of an agar plate 

 culture. The preparation was photographed mounted 

 in canada balsam. 



Figs. 10, 11. o, coccoid cell with a single, diagonally 

 placed chromatinic body, b, cell with two chromatinic 

 bodies resulting from recent longitudinal division, 

 c, division of this bacterium will give rise to two single 

 cells (stage c' of Text-fig. 1), in contrast to the more 

 usual mode of division at the four-cell stage, illustrated 

 by the dividing bacterium above d in PI. 6, fig. 13. 

 Fig. 12. In the centre are two young rod forms with 

 clearly defined dumbbell bodies. In the one on the 

 right a rounded faintly stained body is visible between 

 the chromatinic dumbbell bodies, similar to /, fig. 1 

 and c, fig. 2, PI. 5. 



Plate 6. Proteus vulgaris, Bact. coli, B. mesentericus 



All figures except fig. 18 are from preparations mounted 

 in water. Fig. 18 is the same as the top part of fig. 29, 

 PI. 8 and is from a Bouin-Giemsa preparation mounted 

 in canada balsam. 



Figs. 13, 14. From one culture. Fig. 1 3 shows the short 

 normal bacteria from the raised edge of an agar 

 culture shortly before swarming was due to begin. 



Fig. 14. From an impression preparation made after 

 swarming had been in progress for 1 hr. In fig. 13 

 particularly clear division stages at a and b ; c and d 

 illustrate further stages in the formation of two-cell 



bacteria with four chromatinic bodies. In fig. 14 

 four compact, symmetrically arranged chromatinic 

 configurations are visible in the larger bacterium 

 marked a. Many of the chromatinic structures in the 

 long filaments are very broad, which suggests that 

 they may be composed of several pairs of dumbbell 

 bodies. At b a large filament is seen to break into two 

 fragments of equal length. A delicate strand of chro- 

 matinic matter connects the first two chromatinic 

 structures from the left, in the left daughter bacterium. 



Fig. 15. A two-cell rod of B. mesentericus containing 

 two pairs of closely contiguous, symmetrically built 

 dumbbell bodies separated by a median cytoplasmic 

 cell boundary. The shadows on top of the bacillus are 

 discarded spore cases. 



Fig. 16. An early stage in the separation of the closely 

 contiguous dumbbell bodies. Note the well-defined 

 median cell boundary and compare this photograph 

 with 6 in PI. 8, fig. 28. The corresponding stage in the 

 development of Bact. coli is shown in PI. 5, fig. 4. 

 Fig. 16 should also be compared with stage h of 

 Badian's text-fig. 1 (1933). 



Fig. 17. Near the lower edge of the picture a typical 

 composite filament of B. mesentericus from the first 

 2 hr. after spore germination. Note that the middle 

 one of the three septa is particularly deeply stained ; 

 it is here that a break will take place like that illus- 

 trated in fig. 19. There are also clear-cut median cell 

 boundaries in two other bacteria on this picture. 



Fig. 18. Comparison with the previous figure shows 

 that the dark bands in the long bacillus correspond 

 to cell boundaries. No chromatinic structures are 

 shown in fig. 18. 



Fig. 19. See legend of fig. 17. 



Figs. 20. 21. Bact. coli, 4 hr. agar slant at 37° C; 2 hr. 

 in tap water at room temperature, If hr. on fresh 

 nutrient agar at 37° C. (Control to a radiation experi- 

 ment.) The photograph shows slender bacteria typical 

 for growth on crowded plates of more than 2 hr. incu- 

 bation. At a, b and elsewhere two-cell rods with four 

 resting or dividing chromatinic bodies are seen. A 

 slightly constricted two-cell rod with a pair of closely 

 approximated chromatinic bodies in each of its cells 

 is visible in the right-hand bottom corner of fig. 20. 

 To the left of this bacterium, at c, sister bacteria are 

 seen connected by a slender protoplasmic bridge. 

 Compare these two photographs with PI. 7, fig. 24, 

 where the distribution of cell boundaries is shown. 



Plate 7. Bact. coli, B. mycoides 



All figures except figs. 25-27 are from preparations 

 mounted in water. 



Fig. 22. Typical sample of the different types of cells in 

 an 18 hr. 37° C. slant culture, a are coccoid forms 

 with single dumbbell bodies. Compare the poor de- 

 finition of the chromatinic structures in this picture 

 with the strong contrasts between cytoplasm and 

 chromatinic structures in PI. 5, figs. 1, 2. 



Fig. 23. Bacteria from an 18 hr. slant culture, spread 

 on agar, fixed with Bouin's fluid and stained briefly 

 with Giemsa's solution. Except for the darkly stained 

 bacterium with median constriction in the left-hand 



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