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       (5) At least four tubes containing only sterile broth should be inseminated
with 50 cm. of the 1,000,000 dilution of the typhoid culture, in order to control
the certain presence of living bacteria in the quantum added to each tube. In
our experience, however, we have never found that any of these tubes remained
sterile.

       (6) In order to test the sterility of the vaccines, of the serum and of the salt
solution samples of these should always be planted on agar or in broth.

       (7) After the addition of the sterile broth it is necessary to incubate the
tubes for three days, as owing to the inhibitory action of the serum growth may
be considerably delayed.

       As an example of the results which are to be obtained by this method, we
have now to detail comparative observations made with two vaccines, one broth
and one agar, and the sera of three different goats. The vaccines were prepared
as follows:—

       Vaccine I was a broth culture of bacillus typhosus which had been incubated
at 37°C. for four weeks. It was killed by heating in a water bath at 6o°C. for
half an hour.

       Vaccine II was prepared by emulsifying agar cultures, 48 hours old, with
normal salt solution. No attempt was made to measure the amount of the salt
solution used. The bacteria were killed by heating the emulsion at 60°C. for half
an hour.

       These two vaccines were tested side by side, after the manner already
described, against the sera of three different goats.

       The following were the results obtained:—

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