80 THE DISCOVERY OF CHICKEN CHOLERA, ETC. 



and death. This animal may also be infected by the ingestion 

 of food contaminated with a culture of the bacillus. Both in 

 fowls and in rabbits the disease may, under certain circumstances, 

 run a more protracted course ; for instance, when they are 

 inoculated with a small quantity of an attenuated culture. 



It has been repeatedly proved that horses, cattle, sheep, 

 goats, pigs and dogs are naturally immime. 



MOKPHOLOGY. 



The microbe of chicken cholera is one of the smallest germs 

 known, rarely exceeding the ^^Iqq of an inch in length and the 

 30^00 of an inch in diameter ; in fact, it not only requires the 

 use of specially prepared stains and the highest class lenses for 

 its detection, but a certain amount of skill and perseverance in 

 order to understand its morphological characters. 



In cover-glass specimens of blood from an animal dead of 

 septicaemia hemorrhagica, stained with an alkaline solution of 

 methylene blue, the organisms appear when suitably illuminated 

 under an oil immersion lens, as extremely minute slightly oval- 

 shaped cells, the poles or extremities staining very deeply while 

 the central portion remains almost clear. 



They are mostly uniform in size, but more rarely some are 

 seen to be very much longer, taking the stain in a more irregular 

 manner. 



Biological Chaeactees. 



The chicken cholera organism is non-motile, does not form 

 spores, grows in various culture media at the room temperature, 

 but more rapidly at IOC Fahr,, or just above blood heat. It is 

 an aerobic bacterium — that is to say, oxygen is required for its 

 development. 



Upon gelatin plates after three days incubation at 70*^ Fahr., 

 the colonies appear as extremely minute granular spherical 

 white dots, with a more or less irregular outline, and by trans- 

 mitted Ught have a yellowish colour ; later the central portion 

 of the colonies is of a yellowish-brown colour and is surrounded 

 by a transparent peripheral zone. 



In streak cultures upon the surface of sterilised tubes of 

 nutrient agar agar, gelatin or blood serum, the growth is limited 

 to the immediate vicinity of the line of inoculation, and consists 

 of finely granular semi-transparent colonies, which form a thin 



