348 PROTECTIVE INOCULATIONS. 



affected areas Lave a dark color and contain a bloody serum in which 

 the bacillus is found to which the disease is due. This is an an- 

 aerobic bacillus which forms large oval spores. 



The etiology of the disease was first clearly established by the re- 

 searches of Arloing, Cornevin, and Thomas (1880 to 1883), and sub- 

 sequent researches have shown that immunity may be produced in 

 susceptible animals by protective inoculations. 



The disease causes considerable losses among cattle in certain sec- 

 tions. Horses do not contract it spontaneously, and when inoculated 

 with a culture of the bacillus present only a limited local reaction. 

 Swine, dogs, rabbits, fowls, and pigeons have but slight susceptibility. 

 The researches of the authors above mentioned have shown that the 

 virulence of a culture is greatly increased by adding to it twenty per 

 cent of lactic acid. The guinea-pig is the most susceptible animal, 

 and succumbs in from twenty-four to thirty -six hours when inoculated 

 subcutaneously with a small quantity of a pure culture. According 

 to Kitasato cultures in a bouillon made from the flesh of the guinea- 

 pig soon lose their virulence, while cultures in solid media preserve 

 their virulence for a long time. Cultures are readily attenuated by 

 heat, according to the method of Toussaint and Chauveau exposure 

 to a temperature of 42 to 43 C. in the absence of spores. The 

 spores are attenuated by exposure for several hours to a temperature 

 of 80 to 100 C. Arloing, Cornevin, and Thomas recommend for the 

 production of immunity in cattle inoculation with a dried powder of 

 the muscles of animals recently dead from the disease. This is at- 

 tenuated by heat. According to Kitt the muscles should first be 

 dried at 32 to 35 C. and then powdered. Two " vaccines " are pre- 

 pared from this powder a strong vaccine by exposure to a temper- 

 ature of 85 to 90 C. for six hours, and a weaker vaccine by exposure 

 for the same time to a temperature of 100 to 104 C. (dry heat). An 

 inoculation is first made with the weaker vaccine which gives rise to 

 a local reaction of moderate intensity. Later a second inoculation is 

 made with the stronger vaccine, after which the animal is immune 

 from the pathogenic action of the most virulent material. Immunity 

 may also be secured by intravenous injections ; or, in guinea-pigs, by 

 inoculations with cultures which have become attenuated by being kept 

 a few days, or by exposure to a temperature of 42 to 43 C. ; or by 

 inoculation with a very small quantity of a pure culture ; or by inocu- 

 lations with filtered cultures (Eoux and Chamberland) ; or with cultures 

 sterilized by heat (Kitasato). A non-fatal and protectivejocal infec- 

 tion may also be produced in cattle by inoculations with virulent ma- 

 terial made into the extremity of the tail. Eoux has claimed that 



