Microhic Diseases Individually Considered. 175 



quickly kills the microbe, it is in moist poultry pens, 

 in which the excretions accumulate, and in stagnant 

 waters of the yards, that the virus is, for the most 

 part, preserved. The germs of the disease may thus 

 persist for a long time on one farm even after the re- 

 moval of all diseased fowls. 



The microbe of chickeii cholera, being aerobic, ex- 

 tracts the oxygen from the blood and thus determines 

 symptoms of asphyxia, which show themselves by 

 the dark blue color of the comb, general coolness of 

 the body, and hemorrhagic patches on the pericar- 

 dium, liver, peritoneum, etc. By filtering a bouillon 

 culture through plaster of Paris, M. Pasteur has ob- 

 tained a liquid free from germs and which, inoculated 

 to fowls, produces, temporarily, the most prominent 

 symptoms of the disease, giving rise to a condition 

 similar to that which succeeds to the absorption of a 

 narcotic dose of opium. The animal is at first ex- 

 cited, then its feathers become rufiled, the appetite is 

 lost, it becomes somnolent, and, after several hours, 

 emerges from its temporary stupor. Thus we see 

 produced experimentally the intoxication w^hich suc- 

 ceeds to the multiplication of the specific bacteria in 

 the blood. 



Attenuation — Preventive inoculation. — In cultivatinsr 

 the microbe of fowl cholera in the air and inoculatinsr 

 cultures of difierent ages, M. Pasteur observed that 

 their virulence progressively diminished. Thus, by 

 inoculating each time the same number of fowls with 

 virus fifteen days old, one month, two mouths and 

 over, he observed that the mortality induced by these 

 diiferent specimens of virus gradually decreased, and 

 that, at a certain time, all the inoculated fowls sur- 



