ON A EED PIGMENT-FOEMING OEGANISM. 415 



poles. The whole cell is at the same time larger. The central 

 chromatin then shows signs of division, and the two halves 

 gradually separate and travel away from one another towards 

 the poles. Division of the cell takes place between the two 

 halves, and the chromatin is once more equally distributed 

 over the cell. The appearance of constriction in fixed and 

 stained specimens at the central plate is partly artificial, as in 

 organisms examined in a drop culture containing methy- 

 lene blue the outer border of the cell may be made out, pre- 

 serving its original breadth until the division is about to take 

 place. It has already been mentioned that the B. typhosus 

 presents similar appearances to the above, and Babes (' Soc. 

 Anatomique/ December, 1884) figures and describes very simi- 

 lar forms occurring in the comma bacillus of Koch. He states 

 that at first the poles of the cells are deeply stained, but as the 

 organism grows the deeply staining portions pass to the centre 

 and become fused ; and that then a clear space forms, dividing 

 the central mass into two parts, which indicates the com- 

 mencing cell division. 



This organism, when grown under somewhat unfavourable 

 conditions, readily shows involution forms. When grown on 

 gelatine with scanty access of air the cells become three to four 

 times as long as broad without, in many instances, dividing, 

 and after some days become vacuolated. These vacuoles are 

 generally three in number, and symmetrically arranged. This 

 vacuolation explains many of the appearances seen in the 

 stained specimens. The cultures in fluid media, especially in 

 the depths and in sugar-containing fluids, show long, almost 

 leptothrix, forms, and there is a great tendency to the 

 formation of bud-like projections, which in some instances are 

 80 prolonged as to resemble branchings. The protoplasm in 

 these forms also presents irregularities of distribution. 



The following is a short list of the principal red pigment- 

 forming bacilli, with their difi'erential characteristics : 



VOL. XXXII, PART III. — NEW SER E E 



