ANTHRAX. 299 



Immunity and Vaccination. Recovery from malignant 

 pustule does not confer immunity, at least none of any 

 duration. It has been repeatedly observed that the same 

 individual has been attacked two or three times with 

 malignant pustule, and even at intervals of a few months. 

 The second attack often pursues even a more virulent 

 course than the first. Nevertheless, it is possible experi- 

 mentally to immunize animals to anthrax. The anthrax- 

 bacillus is the microbe with which Pasteur demonstrated 

 for the first time that the action of heat diminishes the 

 virulence materially. Pasteur cultivated anthrax-bacilli at 

 a temperature of 42 C. (107.6 F.). They still developed 

 at this temperature, but gradually suffered in virulence from 

 day to day. If after the lapse of several days the bacilli 

 thus attenuated are transferred to a new nutrient medium 

 and are exposed to a more favorable temperature (35 C. 

 95 F.),they then grow luxuriantly again, but their virulence 

 remains attenuated ; the bacilli do not recover. Upon the 

 basis of these fundamental facts Pasteur prepared two 

 varieties of attenuated anthrax-bacilli, one of which had 

 been exposed for from fifteen to twenty days to a tempera- 

 ture of 42 C. (107.6 F.), and which was capable of 

 destroying only guinea-pigs not more than twenty-six hours 

 old (Vaccine I). The other had been exposed from ten to 

 twelve days to a temperature of 42 C. (107.6 F.), and it 

 was capable of destroying guinea-pigs, white mice, and 

 rarely rabbits (Vaccine II). 



According to the method of Pasteur, animals (rabbits, 

 sheep, cows) are inoculated first with Vaccine I. They be- 

 come sick and exhibit fever of greater or less intensity. 

 After the disease-symptoms have disappeared, the animals 

 are inoculated with Vaccine II, and the same symptoms 

 are repeated. After the animals have recovered from this 

 second disturbance they are thoroughly protected against 

 inoculation with highly toxic anthrax-material. 



The attenuated anthrax-cultures generate alkaline sub- 

 stances upon the nutritive media ; whereas the virulent 

 cultures generate a considerable amount of acid. The 

 vaccines are distinguished from the highly virulent cultures, 

 further, by the fact that they give rise to febrile movement. 

 This fact is usually interpreted as indicating that the 

 fever represents a reaction of the organism to the invading 

 parasites. As a matter of fact, it has for a long time been 



