LIFE HISTORY OF BACILLUS ANTHRACIS. 197 



since tlie gigantic discoveries of Harvey or Jenner began to be 

 appreciated. 



After much diligent research, M. Pasteur has arrived at 

 knowledge from which he asserts that the disease-producing 

 germ of anthrax may be so modified by artificial cultivation that 

 healthy animals, inoculated with the attenuated virus, receive 

 a certain immunity from the fatal effects of the disease whether 

 naturally or artificially encountered. 



The following is the method adopted to obtain the inocula- 

 tion-fluid, or, as Pasteur calls it, ' vaccine.' A drop of blood, 

 taken from an animal about to die of anthrax, on a glass rod is, 

 under antiseptic precautions, placed in a small vessel contain- 

 ing some fowl-broth (bouillon de poule), or other suitable 

 pabulum, perfectly clear, and rendered sterile by being pre- 

 viously raised to a temperature of 115° C. If this httle vessel 

 be now kept in pure air at 42° to 43° C, a cloudiness is seen, 

 and cultivation goes on, though no spores are said to be pro- 

 duced (at 45° C. cultivation ceases). In this crop there is a 

 certain amount of attenuation acquired. Now one drop of 

 this crop is introduced into another vessel containing fowl- 

 broth, and placed under the same conditions as the first ; and 

 so the process is repeated until the required number of genera- 

 tions is produced. It is highly essential that the above 

 temperature be maintained in the cultivation, as the vital 

 point, the object of the process, attenuation, rests uj)on it ; 

 namely, that under this circumstance no spores are produced. 

 It is equally important that certain definite periods should 

 elapse between each impregnation, and according to the length 

 of these periods, and the number of sowings, will be the viru- 

 lence of the different cultures. The longer the interval, the 

 less potent will the next cultivation be, and the process will be 

 continued till, by experiment, the required strength is ascer- 

 tained. 



This inoculation-fluid, introduced into the susceptible animal 

 system, is said to produce there such a change as to render it 

 in the majority of cases incapable of contracting anthrax, or, 

 as it were, a certain vis medicatrix is given to the constitu- 

 tion to encounter and resist its effects. The vaccine is 

 generally injected into the subcutaneous tissue, and there may 

 be more or less swelling at the seat of puncture ; by some the 



