BACTERIA 195 



cearum, which is the cause of the " angular spot " disease of the 

 cotton plant. He first observed the presence of deeply-staining 

 structures within the body, especially in cultures more than four 

 days old. 



The bacterium was grown on potato agar or a synthetic medium 

 of K2HPO4(0-l per cent.), KNO3 (0-2 per cent.), MgS04 (0-1 per 

 cent.), NaCl (0-1 per cent.), glucose (1-0 per cent.) and agar (1-5 

 per cent.). The staining technique employed was as follows : 

 chemically-cleaned slides were flamed and a drop of Ziehl carbol- 

 fuchsin (diluted with an equal volume of water) was placed at one 

 end of the slide and a thin film of stain made by drawing the edge 

 of a strip of typewriting paper over the drop and along the slide. 

 For success, the film should dry rapidly and evenly and be barely 

 perceptibly visible when the slide is held up to the light. A small 

 drop of sterile water was now placed on the middle of a flamed 

 thin cover-slip. This was touched with a platinum wire carrying 

 the organisms from the culture, and the cover-slip was then in- 

 verted and dropped on the stained slide. The mount was sealed 

 with vaseline or gold size. The bacteria take up the stain slowly 

 if the film has been correctly prepared. 



In general appearance, in cultures twenty-four hours old, the 

 bacteria show a prej^onderance of slender rods which stain more 

 or less evenly and deeply and vary in size from 1-5 to 4-Oju. by 

 0-5 to 0-9 IX, and are cylindrical with rounded ends. If the stain 

 be not too intense and the slide be examined immediately after 

 preparation and before staining is complete, a number of the 

 cells can be seen to contain a deeply-staining spherical granule 

 (rarely two or more such granules may occasionally be observed). 

 These spherical bodies, as a general rule, are situated towards 

 one end of the cell, and are conspicuous by reason of their 

 greater affinity for the stain. This structure is soon lost to 

 view because the rest of the cell takes up the stain. After the 

 lapse of three to four days, the cells in culture lose their power of 

 staining evenly over their whole surface, and another structure 

 now becomes visible. This body is centrally placed, and shows 

 a different appearance in different cells. Concurrently with the 

 appearance of the central body, the granules previously referred to 



7—2 



