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If symptoms have once occurred, treatment is of no avail. 

 Statistics of the value of the treatment are difficult to obtain, but 

 it is stated that before inoculation was adopted at least ten 

 per cent, of persons bitten by rabid animals succumbed, while 

 since 1886 at the Pasteur Institute the mortality has always 

 been under 1 per cent, in any year, and in every year more 

 than a thousand cases have been treated. 1 



In 1888 a new series of observations were made which threw 

 much light on the problems of immunity. In this year Roux 

 and Yersin discovered diphtheria-toxin, a product of the 

 diphtheria bacillus, and Kitasato discovered tetanus toxin ; and 

 in 1890 Behring discovered in the serum of animals immunised 

 against diphtheria and tetanus, substances which neutralised 

 these toxins, which he called " anti-toxins." This was the 

 foundation of serum therapy. 



In 1890 Koch introduced his "tuberculin," a product of the 

 growth of tubercle bacilli. This was intended for use both as 

 a means of diagnosis and as a cure for tubercular infection. It 

 was not a vaccine, but was used as " toxi-therapy." It was 

 abandoned by Koch in 1897 for other preparations — tuberculin 

 O. and tuberculin R. — which are extracts of the bodies of the 

 bacilli. Tuberculin R. acts as a vaccine. Some very unfor- 

 tunate results attended the early experiments, and the method 

 fell into disuse ; but with accurate methods of estimating the 

 effects of various doses, tuberculin R. has become a remedy 

 of the first importance. 1 Recently a " bacillary emulsion " has 

 been introduced, which approximates still more closely to 

 ordinary vaccines. 



Further notable experiments in prophylactic inoculation 

 are those of Ferran and also Haffkine with cholera, and of 

 Haffkine with plague. In 1897 Haffkine inoculated himself 

 with a sterilised bouillon culture of the bacillus pestis, and 

 it has since been extensively used in India. Statistics show 

 that a partial immunity is conferred by this treatment. 



The most important prophylactic measure of recent years 

 is that introduced by Wright against typhoid fever. Some 

 large figures are available by which to judge of its efficacy. 

 During the South African War about 19,000 men in South 

 Africa and India were inoculated. Of these 1 in 84 was infected, 

 with a case-mortality of 17 per cent. At the same time, among 



1 Bosanquet. 



