E. M. Doidge 121 



from an agar streak 1 to 4 days old; the rods occur singly, in pairs or 

 in short chains, and the motion consists of darting or tumbling move- 

 ments. The single rods do not progress far in one direction but make 

 short, swift darts interrupted by tumbling movements. The chains 

 move forward in a sinuous manner. 



Examination with the dark ground illumination shows that the 

 flagella are polar and that they are at the forward end of the rod as it 

 moves. 



These flagella stain readily by Ellis's modification of Loeffler's 

 method. In the first preparation the majority of the rods showed two, 

 three and four flagella, and, since Smith (8) describes the organism as 

 possessing one polar flagellum and sometimes two, a large number of 

 slides were prepared from different cultures. In these over 50 % of 

 the rods had four flagella, a large number two or three, and a small 

 minority had one only (Plate XXIV, fig. A). From the cultural characters 

 it seems certain that the organism is the one described as Bacterium 

 mori and this is the only morphological difference observed. Possibly 

 when differently treated some of the flagella are dropped, but as Smith 

 does not mention by which method his flagella were stained I was 

 unable to ascertain whether this was the explanation. 



The rods stain readily with carbol fuchsin and other aniline dyes 

 but are Gram-negative. Involution forms were observed in broth 

 containing 6 % NaCl. 



Cultural Characters, etc. 



Colonies on (+ 15) nutrient agar are barely visible to the naked eye 

 after 24 hours at 25° C. After 48 hours they are round and white 

 with a smooth margin ; the margin subsequently becomes undulate. 

 Surface colonies attain to a diameter of over 1 cm. in thinly sown plates, 

 but the size is much affected by crowding. The internal structure of 

 the colonies is at first homogeneous and later firmly granular. Sub- 

 merged colonies remain very small and irregular in outline. 



Nutrient agar streak. On slant agar (+15) there is a fair amount of 

 growth which is smooth, white, flat and spreading with an entire margin. 

 It is translucent, slimy and odourless ; the medium is not stained. 



Nutrient agar stab. A very thin white line of growth follows the 

 needle track ; the best growth is at the top. 



Nutrient gelatine colonies (+15) are flat, white, slow-growing, more 

 or less round; the margin is at first smooth then undulate-lobulate; 

 no liquefaction. 



