MICROBIAL DISEASES OF MAN AND ANIMALS. 605 



of them. Thus a satisfactory method is at hand for determining, without 

 injury to the birds, which hens are infected with Bad. pullorum, and 

 consequently are the source of infection, if their eggs are used for hatching 

 purposes. 



Quite recently a pullet which was less than eight months old, 

 and which was one of the survivors of an infected flock, showed the pres- 

 ence of the specific bacterium in the ovary. This discovery completed 

 the cycle of infection. The laying hen is a " bacterium-carrier." Her 

 eggs harbor the bacteria, and the chicks which are hatched emerge with 

 the organism planted within them. These chicks are the source of in- 

 fection of other chicks which are normal at the time of hatching. The 

 disease becomes epidemic. The female chicks which survive carry the 

 infection in their body until they are mature laying hens, and the same 

 cycle is begun again, unless intelligent steps are taken to eradicate the 

 infection by methods which are most obvious. 



CHICKEN CHOLERA.* 



Bacterium cholera gallinarum. 



The bacterium causing this disease was first noticed by Perron- 

 cito and Toussaint; later, in 1880, it was described by Pasteur, and 

 was the first organism in which the French savant succeeded in atten- 

 uating the virulence and the first disease, for which a vaccine made 

 from attenuated organisms was prepared. Koch in 1878 described an 

 organism of similar pathogenicity as the bacterium of rabbit septicaemia 

 and in 1886 the term hemorrhagic septicaemia was given by Hueppe to a 

 number of infectious diseases of the lower animals in which hemorrhagic 

 spots were found in the tissues and internal organs. In 1900 Lignieres 

 discussed these bacteria, and named them as a genus, Pasteur ellose, the 

 specific name given depending on the animal for which it was most 

 pathogenic. Thus he distinguished avian, porcine, ovine, bovine, 

 equine and canine Pasteut -elloses. 



The specific characters of this group are small ovoid bacteria, often showing bipolar 

 staining when treated with the aniline dyes, non-motile, no spores, Gram-negative, 

 polymorphic, not liquefying gelatin, no visible growth on naturally acid potato, milk 

 unchanged, no indol production, generally aerobic but also a facultative anaerobe, viru- 

 lence changeable, but usually very pronounced. 



* Prepared by F. C. Harrison. 



