PROTECTIVE INOCULATIONS. 305 



from three to four days. The symptoms following- the second inoculation 

 were generally rather more marked, but of shorter duration. The whole 

 recalls the sensation of a bad cold in the head, lasting about one or two days. 



"The microbes introduced under the skin do not propagate, but after a 

 certain time they die and disappear. It is the substances which they contain, 

 and which are set free when they die, that act upon the animal organism and 

 confer immunity upon it. It is found that the same result can be obtained if 

 the microbe be killed before inoculation, and if their dead bodies only be in- 

 jected. Thus I have been enabled to prepare vaccines preserved in weak 

 solutions of carbolic acid. In this the microbes die at the end of several 

 hours, and the vaccine so prepared has been found still efficacious six 

 months after its preparation. It is evident that there is much advantage in 

 this state of preservation of the microbes. They can be used by persons 

 having 110 bacteriological training, and the absence of every living organism 

 makes them perfectly safe. The carbolic acid that they contain preserves 

 them against any invasion of other microbes. Finally, as they can be kept 

 for several months, their preparation can be entrusted to a central laboratory, 

 whence the vaccine ampoules can be sent out to operators. But it may be 

 presumed that immunity given by these preserved vaccines will not equal in 

 persistency that produced by living ones, and as the method is not yet backed 

 up by established statistics, it is better that vaccinations should be done as 

 much as possible with living virus, so as to obtain the most conclusive 

 results. 



"As to the length of time that immunity produced by living vaccine 

 lasts, we have not yet at the laboratory animals that have been inoculated at 

 a very distant date ; those upon which we experimented dated from, at most, 

 four months and a half. At the end of this time their immunity was found 

 to be still perfect, and we do not despair of its lasting much longer yet. 



" HARMLESSNESS OF THE METHOD. 



"The inoculations upon man, added to the hundreds of experiments that 

 we have made upon animals, testify to the perfect harmlessness of these 

 operations, and there is no difficulty in proving their efficacy by experiment, 

 no matter on what species of animal. We have taken twelve guinea-pigs, 

 and vaccinated six of them with vaccines preserved in carbolic acid since 

 September 8th last. Yesterday, at five o'clock, six days after the first vacci- 

 nation, we injected into the peritoneal cavity of all the non- vaccinated ani- 

 mals a fatal dose of virus, and into the vaccinated animals we injected a 

 double dose. The six vaccinated animals are perfectly well, while of the 

 others two have already died of choleraic poisoning, two are very ill, and the 

 others will certainly soon become so. But it is evident that I cannot perform 

 a like experiment on man (but, however, this would be the only means of 

 being able to give a definite experimental demonstration)/' 



Further details as to the method are given by Woodhead in the 

 "Edinburgh Hospital Keports," as follows: 



"In order to be absolutely certain that the virus is pure, M. Haffkine 

 makes cultivations before each inoculation of the human subject, by Roux 

 and Yersin's method, one devised for the separation of the diphtheria bacillus. 

 A small drop of the virus exalte is taken on a spatula-shaped needle, and 

 streak after streak is made with the flat of this needle on the surface of the 

 agar in the tubes, a couple of tubes being used, so that twelve streaks per- 

 haps, in all, are made without the needle being recharged ; in the earlier 

 streaks, of course, the seed bacilli are so close together that a continuous line 

 of colonies makes its appearance ; but along the course of the later streaks, 

 colonies, with distinct intervals between them, are developed ; part of one of 

 these is examined under the microscope, in order to determine that it is made 

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