150 AIDS TO BACTERIOLOGY 



infection may sometimes cause the disease, food contain- 

 ing virulent material is a very important factor in its 

 dissemination. Ewes, goats, bitches, and guinea-pigs can 

 be infected experimentally. 



Non-pregnant cattle have been immunised by means 

 of large doses of the living cultures of the abortion bacillus, 

 and treatment of infected cattle by vaccines gave very 

 promising results. Stockman thinks abortions can be 

 reduced from the 30 per cent, that sometimes occur to 

 6 or 7 per cent, by prophylactic inoculation. 



CHAPTER XIII 

 THE SPIRILLA 



The Spirillum of Asiatic Cholera. 



Morphology. Spirillum cholerce Asiatics (Koch's ' comma' 

 bacillus), as it appears in the excreta, is a curved rod 

 ('vibrio'), 2 //, by 0-3 JLL. On cultivation, especially in 

 liquid media, S-shaped and spirillar forms develop. 

 It is actively motile, with a single flagellum at one end 

 only, exceptionally more. No spores are formed. Desic- 

 cation and sunlight are rapidly fatal, and its thermal 

 death-point is about 50 C. The organism is Gram- 

 negative, but is readily stained with anilin dyes, especially 

 with dilute carbol-fuchsin. 



Cultural Characters. The spirillum grows readily on 

 most media. An alkaline reaction is essential, develop- 

 ment being hindered by small amounts of acid. Aerobic 

 conditions allow a much better growth than anaerobic 

 ones, and its resistance to disinfectants increases as a 

 saprophytic habit develops. 



It slowly liquefies gelatin, giving in a stab culture in 

 forty-eight hours a bubble of liquefaction at the top of 

 the stab only. While growing on most media at 22 C., 

 on potato there is no perceptible growth at this tempera- 

 ture. On potato at 37 C. there is a slow, light greyish- 

 brown growth. 



The rapid formation of indole is very characteristic of 

 Koch's comma. It gives a creamy growth on agar and 



