Dorothy M. (Jaylky 467 



milk. It was not until the development of the living oval bodies into 

 the long rod stage was watched under the microscope that it could be 

 definitely proved that both forms were stages of the same organism 

 (see Plate VII, figs. 1—10). 



A thin film of acid pea agar agar (1 per cent, normal HCl) was obtained 

 by infecting the medium with a pure culture of Ps. seminum, and 

 then before the medium had time to solidify, a sterile coverslip was 

 dipped into it, so that only one side touched the medium. The cover- 

 slip was then placed on a sterilised moist-chamber sunk slide, and fixed 

 in position by two or three drops of paraffin wax. The slide was then 

 placed upon a warm stage and kept under observation for twelve hours. 

 Owing to the layer of air between the coversKp and the slide the dark 

 ground illumination substage could not be used. However, by careful 

 adjustment, it was possible to get a satisfactory lighting. Unfortu- 

 nately, after twelve hours the coverslip was cracked while focusing, 

 so that details of the beading stage, which, it will be noticed is just 

 beginning in /group, Plate VII, fig. 10, could not be followed out. In a 

 hanging drop the organism tends to become more and more difficult 

 to see the older it grows. One rather interesting point to be noticed in 

 these figures is that, when division is completed, the full-grown daughter 

 rods come to lie parallel to one another instead of end to end, Plate VII, 

 figs. 4—10. 



This suggests that the daughter rods grow in length in the region 

 somewhere near the point of division, especially as, in this case, the 

 organism is growing on a solid agar medium, in which entire change 

 of position would not be easy. The bending of the rod before complete 

 division also rather supports this suggestion. In one case, e, it will 

 be observed that complete separation has not occurred until the third 

 division, and the rods lie end to end. It is only in fig. 8, that the marked 

 bending appears in this group. Group e is not figured in figures 9 and 10 

 as it grew too large for the whole of it to appear within the field of the 

 microscope, and also became overgrown by a neighbouring group outside 

 the field. I venture to suggest that these observations, together with 

 other factors, may account for the puzzling variability of the macroscopic 

 appearance of the colonies. There were slight indications from time 

 to time of the formation of thin capsules surrounding the rods, but with 

 regard to this the lighting did not allow of any very accurate observations. 

 These capsules, however, have been observed in stained sections. 

 Smears of old cultures on solid media, stained for spores, do not give 

 any very satisfactory results, as the organism gets massed together 



Journ. of Asric. Sci. viii 31 



