PROTECTIVE INOCULATIONS. 805 
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. Itis 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 no 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 toa 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 
avery 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 Reports,” as follows: 
‘‘TIn 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 exalté 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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