PROTECTIVE IMMUNIZATION AMONG THE LOWER ANIMALS 701 



receive a lethal dose of the fully virulent anthrax. He declared that 

 the 25 non-vaccinated sheep would die, whereas the 25 vaccinated would 

 remain alive and well. The remaining 10 sheep were to serve as controls. 



The challenge and its acceptance were widely advertised in the 

 journals, and Pasteur was made the subject for many witticisms. Ex- 

 citement ran high, and a large crowd, comprised of physicians, veterin- 

 ary surgeons, journalists, farmers, etc., accompanied Pasteur to the 

 farm (Pouilly le Fort) where he was to make the final test by inoculating 

 the deadly anthrax. One vaccinated animal developed a temperature 

 overnight, a fact that caused Pasteur much anxiety. On going to the 

 farm the next day, however, again followed by the crowd, he found all 

 the vaccinated animals well! Of the unvaccinated, 22 were dead, and 

 the others died during the following night. Pasteur's triumph was 

 complete, and the possibility of preventive vaccination was demonstrated 

 to the world. 



The vaccine is prepared of attenuated cultures of virulent anthrax 

 bacilli. 



Vaccine No. 1 is weakest or lowest in virulence, and the first to be 

 injected. This vaccine is prepared by growing virulent anthrax bacilli 

 at a temperature of 42 C. for from six to ten weeks, or until tV loopful 

 of the culture, when injected into rabbits, guinea-pigs, and mice, will 

 show virulence for mice only, but not for guinea-pigs and rabbits. 



Vaccine No. 2 is prepared by growing virulent anthrax bacilli at 

 42 C. for about twenty days, or until tV loopful is virulent for mice, 

 partly so for guinea-pigs, and not at all for rabbits. 



Vaccine No. 3 is not generally used except for immunizing sheep and 

 goats. When, however, it is required, it is made as follows: Virulent 

 anthrax bacilli are grown at 42 C. until yV loopful, when injected into 

 mice, guinea-pigs, and rabbits, will be virulent for all the mice, all the 

 guinea-pigs, and some of the rabbits. 



The vaccines are prepared in ampules containing 1 c.c. of the emul- 

 sion, each representing one dose, to be injected subcutaneously. Vac- 

 cine No. 2 is injected twelve days after Vaccine No. 1, and No. 3 after 

 the same interval following Vaccine No. 2. The resulting immunity 

 usually lasts about six months. 



In instances where it is desirable to immunize a herd before turning 

 them out to pasture on infected areas it is well to inoculate the animals 

 in the early spring, keeping them in the stable during the time required 

 for at least two vaccinations, for the reason that, immediately after 

 vaccination, the animals may become hypersusceptible to infection. 



