BACILLUS ANTHRACIS. 131 



subsequently grown when brought in a suitable medium. 

 The spores resist a freezing temperature, and even the tem- 

 perature of liquid air, for almost an indefinite time. They 

 are killed by dry heat at a temperature of 140 C. only after 

 three hours' exposure, and at 150 C. only after one hour's 

 exposure. By moist heat at the temperature of 100 C. they 

 are killed in from three to four minutes. They resist the 

 action of 5 per cent, carbolic acid for five minutes. 



Its non-sporing forms are killed by a temperature of 54 C. 



Pathogenesis. Cattle, sheep, horses, mice, guinea-pigs, and 

 rabbits are all susceptible to the action of the bacilli. Am- 

 phibia, dogs, white rats, and birds are not susceptible. Sus- 

 ceptible animals may be infected in one of four ways : through 

 the abrasions of the skin and mucous surfaces, through the 

 respiratory tract, through the alimentary tract, or by subcu- 

 taneous inoculation, as generally practised in the laboratory. 



When the bacillus is inoculated subcutaneously into animals, 

 the animal shows little or no inflammation at the point of 

 inoculation, but marked oadema of the subcutaneous tissue at 

 a distance from the inoculating point, with small points of 

 blood extravasation in this tissue. To the naked eye there 

 is very little change in the internal organs except in the spleen, 

 which is enlarged, darker, and soft. Bacilli may be found 

 everywhere in the capillaries, in organs and blood, but espe- 

 cially in the vessels of the lungs, the liver, and in the glom- 

 eruli of the kidneys. Death takes place in from one to three 

 days according to the size of the animal and the dose given. 



The most susceptible animal is the mouse, next comes the 

 guinea-pig, and then the rabbit, and so uniformly is the 

 resistance of these animals shown to the action of inocula- 

 tions with anthrax that the virulence of attenuated cultures 

 used for protective inoculations are tested on those animals. 



Immunization. Pasteur has demonstrated that attenuated 

 cultures of the Bacillus anthracis when injected into susceptible 

 animals are capable of protecting the same against the action 

 of the virulent bacillus, subsequently inoculated, and against 

 an attack of the disease itself. His inoculation or vaccination 

 consists in using cultures that have been attenuated by means 



