EXPERIMENTS IN VACCINATION AGAINST ANTHRAX. 3 



ceclure of the vaccination for this purpose. Pasteur proved that 

 anthrax bacilli when cultivated at a temperature of from 42° to 43° 

 C. will gradually lose their virulence, and also that when removed 

 from such an attenuating temperature and cultivated under normal 

 incubation temperature they will not change their pathogenicity. 

 Thus cultures attenuated for 24 days will be pathogenic for mice 

 but not for guinea pigs and rabbits, wmereas if attenuated for only 

 12 days at the higher temperature they will be virulent for mice 

 and guinea pigs but not for large rabbits. The attenuated cultures 

 will retain their reduced virulence under ordinary conditions, and 

 only in very exceptional instances has any increase of virulence 

 been observed. This characteristic of the anthrax bacillus led Pas- 

 teur to employ the attenuated forms of the anthrax cultures for 

 vaccination purposes. Accordingly he prepared a weakened vac- 

 cine from cultures which had been attenuated for 24 days (premiei* 

 vaccin), and for a second injection cultures which had been attenu- 

 ated for 12 days (deuxieme vaccin). In the epoch-making demon- 

 stration at Pouilly le Fort, before a commission appointed by the 

 French Government, he successfully demonstrated its effectiveness 

 on sheep and cattle. In this instance the vaccinated animals with- 

 stood the injection of virulent anthrax bacilli, w T hereas the controls 

 died. Since that time vaccination against anthrax by the Pasteur 

 method has been very extensively employed throughout the world. 

 Many millions of animals have been vaccinated by this method, and 

 the results in general must be considered very favorable. 



At the same time it must be acknowledged that in vaccination by 

 .the Pasteur method it is essential to have a potent vaccine and one 

 which is properly tested for its pathogenicity. There are disad- 

 vantages in this method of vaccination and these must be given due 

 consideration. The unstable keeping quality of the Pasteur vaccine 

 is a very important factor to be considered. Experience in this line 

 has proved that Pasteur vaccine may deteriorate within a very short 

 time after its preparation, and this has also been demonstrated during 

 the work of the Bureau of Animal Industry in the control of the 

 manufacture of biological products, when periodical tests were 

 undertaken with those of various manufacturers. In repeated in- 

 stances a vaccine proved inert within three months of its preparation. 

 At other times it remained potent for a period of a year. This no 

 doubt is due to the method of preserving and handling the product. 

 When exposed to light and warm temperature it deteriorates very 

 rapdily, and when it is considered that the products of manufacturers 

 may be stored under unfavorable conditions in branch houses and on 

 the shelves in rural drug stores the loss of potency can be readily 

 explained. For this reason it seems wise to reduce the time limit for 



