BE SEARCH IN MEDICINE 17 



Jenner's vaccine was a transmitted cowpox did not militate against the 

 general theory of protecting the individual against a severe form of a 

 disease by the production of a mild form, for cowpox was generally 

 considered to be smallpox modified by passage through another host, 

 the bovine animal. If such results could be obtained against a disease, 

 small-pox, the causal agent of which was unknown, how much easier 

 to vaccinate against a disease of known etiology ! 



This was therefore the first line of attack in the battle for a spe- 

 cific therapy of the infectious diseases. Already Pasteur was at work. 

 An epidemic of chicken-cholera, in 1880, offered the opportunity for 

 extended experiments. In the course of this work, a chance observa- 

 tion gave him the clue to vaccination with bacteria of attenuated viru- 

 lence. It had been his routine practise in the experimental production 

 of chicken cholera to use fresh 24-hour cultures ; these always produced 

 the disease readily. But in the course of the work it happened that an 

 old culture which had been set aside for a few weeks and forgotten, 

 was used, with the unexpected result that the inoculated hens, although 

 ill for a while, promptly recovered, and what was more surprising, re- 

 mained refractory to subsequent inoculation of fresh cultures, though 

 the same cultures were virulent for untreated hens. This phenomenon, 

 the attenuation of virulence clue to artificial cultivation, Pasteur used 

 as the basis of a treatment by vaccination, which had the immediate 

 effect (1880) of reducing the mortality of chicken cholera to one per 

 cent, and the more remote but far more important effect of stimu- 

 lating the study of specific therapy. Incidentally it was the link be- 

 tween Lady Mary Wortley Montagu's preventive inoculation and Jen- 

 ner's vaccination, on the one hand, and modern theories of the produc- 

 tion of immunity on the other. 



The next step was with anthrax, a disease, of cattle. The attenua- 

 tion of chicken cholera virus had been due to artificial cultivation, but 

 about this time Toussaint, of the veterinary school of Toulouse, made 

 some observation on the attenuation of anthrax bacilli under the influ- 

 ence of increased temperature (heating to 55° C. for ten minutes). 

 His observations, however, were without constant results. Pasteur, who 

 was familiar with Toussaint's work, took up the matter and after a thor- 

 ough investigation found that anthrax bacilli cultivated at a temperature 

 of 42° to 43° C, became attenuated, and this attenuation persisted on 

 artificial cultivation (1881). The inoculation of such organisms did 

 not cause anthrax, and when later virulent bacilli of anthrax were in- 

 oculated, the animals were found to be immune. This was the scien- 

 tific basis of the celebrated public test at Melun. Sixty sheep and ten 

 cows were placed at the disposal of Pasteur; twenty-five of the sheep 

 and six of the cows were to be vaccinated with attenuated anthrax 

 bacilli, and after an interval of twelve to fifteen days this was to be 



VOL. LXXXI. — 2. 



