EXPERIMENTS ON THE ATTENUATION OF HOG CHOLERA BACILLI 



BY HEAT. 



INVESTIGATIONS OF 1888. 



Heat has been used by Pasteur in the attenuation of anthrax virus 

 by exposing cultures of anthrax bacilli to a temperature of 42-43 C. 

 continuously for a certain number of days. Cultures kept in a ther- 

 mostat at this temperature for about thirty-one days were so attenu- 

 ated that they were incapable of destroying animals larger than very 

 young mice. Kept in the same conditions for only twelve days, in- 

 oculation failed to destroy adult guinea pigs.* The former culture 

 was denominated the first, the latter the second vaccine. To make 

 sheep immune they were inoculated subcutaneously with the first 

 vaccine and twelve days later with the second vaccine. Subsequent 

 inoculation with strong virus had no effect upon the vaccinated ani- 

 mals, although it was quite invariably fatal to those which had not 

 been so treated. 



Although Pasteur's discovery must be considered a scientific event 

 of great importance, its practical application is by no means a per- 

 fect success. Experiments conducted by Koch, Gaffky, and Loffler, 

 in Berlin, have shown that the process of attenuation does not always 

 go on uniformly, and that the strength of the vaccine can not always 

 be relied upon. A few animals may die as a result of the first or 

 second inoculation. This fact induced the last international con- 

 gress of hygiene at Vienna to adopt the resolution that anthrax vac- 

 cination should not be practiced upon sheep in any locality unless 

 the disease causes .a loss of 2 to 3 per cent, annually. It was also 

 shown in the experiments at Berlin that immunity after vaccination 

 is not absolutely perfect when the virus is introduced with the food. 

 This is perhaps the most common way in which infection takes place. 



The results obtained by Pasteur are sufficiently valuable to make 

 it at least desirable to try heat attenuation for other bacterial organ- 

 isms, although it does not follow by any means that the same proc- 

 ess will suffice for all or even a small number of disease germs, for 

 these differ among one another very widely. 



Kittf has tried heat in the attenuation of the virus of Black Quar- 

 ter in Germany by exposing the diseased muscular tissue, which had 

 been thoroughly dried in the air and ground to a fine powder, to the 

 steam of boiling water at 100 C. for four, five, and six hours con- 

 tinuously. The spores of the bacilli of this disease were sufficiently 

 attenuated after a six hours' exposure so that sheep inoculated with 

 the powder in certain doses remained well after inoculation with 

 strong virus. The reaction after the vaccinal inoculation was very 

 slight. Hog cholera virus is destroyed by a fifteen to twenty min- 

 utes' exposure in a water bath at 58 C. A momentary contact with 

 boiling water is sufficient to destroy it, so that Kitt's method is not 

 applicable to it but only to bacteria which form spores. 



The following experiments were undertaken with a view to test 

 the method of Pasteur on hog cholera bacilli, and to obtain, if pos- 



*Compt.Rend. Acad.des Sciences, March 21, 1881. 

 t Centralbl. f. Bakteriologie u. Parasitenlcunde, 1888, i, 571. 

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