208 Chapter VIII 



[219] series of discoveries, which have opened up a path so fruitful to 

 science and medical art, was the discovery of the attenuation of 

 micro-organisms. The small cocco-bacillus of fowl-cholera after 

 several weeks' culture in broth was found to have become markedly 

 attenuated in virulence. To Pasteur the idea occurred of testing 

 whether fowls that had resisted the inoculation of these attenuated 

 organisms had acquired any real immunity against virulent fowl- 

 cholera. Experiment confirmed his expectation and led to the 

 discovery of the vaccine against this disease. The method was at 

 once applied to other infective epizootic diseases and shortly after- 

 wards Pasteur, Chamberland and Roux found a method of preserving 

 sheep and cattle from anthrax. To attain this end it was found 

 necessary to prevent the bacillus from producing spores (in this they 

 succeeded by cultivating it in broth at a temperature of 42*5 C.), 

 because these spores fix the virulence and prevent attenuation. Having 

 overcome this main obstacle, Pasteur and his collaborators found 

 that their cultures, thus deprived of spores, become attenuated on 

 exposure to the air and so become transformed into vaccines. They 

 were thus able to prepare their two anthrax vaccines which soon 

 found such wide application in practice. A few years later, Pasteur 

 and Thuillier discovered the vaccines against swine erysipelas and, 

 in collaboration with Roux and Grancher, Pasteur made the first 

 application of his discoveries to the vaccination of man against 

 rabies. 



The path thus opened up was traversed by many other investi- 

 gators and led to many very remarkable discoveries. Vaccination 

 with micro-organisms became a recognised method and in the hands 

 of Arloing, Cornevin and Thomas, soon found its application to 

 symptomatic anthrax. The next step in this onward progress of 

 science was taken when Salmon and Smith, working at hog- 

 cholera, demonstrated the possibility of vaccinating not only with hog- 

 cholera bacilli, but also with culture fluids in which these organisms 

 had developed. These fluids, when completely deprived of micro- 

 organisms by filtration, protected the experimental animals from 

 virulent hog-cholera. This discovery, at first sceptically received, 

 was soon confirmed and extended by the work of other investigators. 

 Beumer and Peiper extended it to the experimental disease set up 

 by the typhoid bacillus in small laboratory animals ; Charrin applied 

 it to the disease that he produced by means of the bacillus of blue 



[220] pus ; and Chamberland and Roux prepared vaccines from the soluble 



