Bacteriology and Its Significance 41 



Another phase of this came up in 1795 when Jenner, who was 

 trained by John Hunter, noticed the absence of smallpox among those 

 having had cowpox. He mentioned it to Hunter whose famous reply 

 was "don't talk, try". This led to our modern practice of vaccination 

 against smallpox, a blessing with which we are all familiar. 



This principle of protecting against disease (vaccination) was ad- 

 vanced by Pasteur almost a century later; a little over 40 years ago. It 

 was discovered quite accidentally in 1880 by Pasteur and his assistants 

 while they were working with the germ of chicken cholera. The experi- 

 ments were set aside during the summer vacation after which the cul- 

 tures were found to be markedly changed as to their disease-producing 

 qualities. 



Since cowpox, which is a modified or weakened (attenuated) form 

 of smallpox, protects against the disease of smallpox, Pasteur reasoned 

 that immunity to other diseases might be likewise brought about. Acting 

 upon this assumption, Pasteur attempted to protect fowl against chicken 

 cholera by first inoculating them with an attenuated specific culture. 

 He was able not only to induce immunity against this diseases but 

 later successfully vaccinated against other diseases such as anthrax, 

 and swine erysipelas. 



Pasteur discovered that the pathogenic properties of a parasite 

 toward its natural host might also become changed by serial passage 

 through other animals; by desiccation as well as by other means. 



He utilized these two principles to protect man against the dread- 

 fully fatal disease of rabies. This often is spoken of as the crowning 

 achievement of his 30 years of constant work. By repeated passage 

 (270) through the rabbit of the "street virus" type of the disease, which 

 had a marked varying period of incubation, he was able to standardize 

 the rabic virus so that it killed this animal uniformly in six to seven 

 days. Immunity was produced by several injections of a suspension 

 made of the spinal cord which had been previously attenuated by drying 

 over caustic soda. 



Soule, aware of the fact that in the early times in India and 

 Africa, natives were protected against the ill effects of snake bites 

 with small amounts of snake venom, in 1885 found that when susceptible 

 animals were repeatedly injected with sub-lethal doses of the venom that 

 an increased tolerance for the poison and a relative immunity was 

 gradually built up. This was the first experimental evidence of such 

 protection. 



In the following year Smith and Salmon first demonstrated that 

 dead cultures upon inoculation induced immunity also. 



In the same year Roux and Chamberlain used dead cultures of 

 symptomatic anthrax and obtained protection. 



It was also found that in some cases equally good results ensued 

 by injecting filtered culture fluids devoid of bacteria (filtrate). 



In 1888 Roux, Yersin and Martin made a classical study of diph- 

 theria. They showed the exact relation of the bacillus to the disease 

 and demonstrated the existence of the soluble toxin. This work led 

 directly to antitoxic immunity. 



