1895. LOUIS PASTEUR. 3^7 



— can doubt that the development of modern bacteriology is owing 

 in far larger share to the labours of the German scientist. 



There is, however, one great branch of bacteriological study with 

 which Pasteur's name will be for ever associated. He, first of all 

 men, conceived and carried out the attenuation of the living virus of a 

 disease and practically applied it for the purpose of protective 

 inoculation. The methods which he employed are a matter of history : 

 they may be superseded by better methods, but nothing can detract 

 from this crowning service of Pasteur to medicine. His earlier efforts 

 in this direction were naturally made upon animals, since in them 

 only could rigid experimentation confirm the truth of his views. The 

 results, in the cases of anthrax, fowl-cholera and swine-erysipelas, 

 were successful : it was found possible by inoculation with a culture 

 of mitigated virulence to produce a mild and non-fatal attack of the 

 disease, which nevertheless protected against the effects of cultures of 

 high virulence. The advantages thus offered to farmers and breeders 

 of animals have been largely made use of in infected districts, but it 

 must be confessed that the expectations which were at first raised 

 have not been completely fulfilled. In the case of anthrax, for 

 instance, it has been found so difficult to produce a " vaccine " of 

 uniform strength that a certain proportion of the inoculated animals 

 die, while others are found insufficiently protected. In spite of this, 

 the method is still employed, especially in infected districts, and with 

 good result. The extension of this method to the treatment of 

 hydrophobia in man was Pasteur's next step, and certainly constitutes 

 the most striking direct clinical application of his discoveries. The 

 absence of any demonstrable microbe in rabies and the impossibility 

 of cultivating the virus outside the animal body were grave difficulties 

 in his way, but these were overcome. Until Pasteur took up the 

 subject, there was no, sure pathological or clinical criterion of what 

 was, or was not, rabies. He showed that by inoculation of portions 

 of the spinal cord of an affected animal into the central nervous system 

 in rabbits the disease could be surely reproduced, thus affording a 

 decisive test as to the nature of any given case. This, from every 

 point of view, was a discovery of the highest moment, and it was 

 followed by the further discovery that the spinal cords of affected 

 animals gradually lost their virulence on drying. The application of 

 the principle of protective inoculation was then easy, but became at 

 once of greatly increased value when it was found that protection was 

 afforded by inoculation of the mitigated virus, even after infection 

 from a rabid animal. From these observations has arisen the 

 system of anti-rabic inoculation now practised at the Institut Pasteur 

 and similar institutions elsewhere. Much vilification has been heaped 

 on its author's head by his opponents, and it must be admitted that 

 the system is still on its trial. In attempting to criticise its results 

 the primary difficulty encountered is that we have no accurate statistics 

 of rabies mortality from which we can start. The mortality among 



