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3, THE MEASURE OF IMMUNITY AGAINST RABIES IN HUMAN BEINGS.
BY
j. W. CORNWALL AND M. KESAVA PAT.
It seemed a matter of considerable importance to endeavour to ascertain whether persons
who have undergone the Pasteurian treatment or its modifications after having been. bitten by a
rabid animal are sufficiently immunised or not. It is probable that individuals differ considerably
in the degree in which they react to the stimulus of the injections, just as has been found to be
the case with animals which have been inoculated for the purpose of obtaining antitoxic or
bactericidal serums.
At the present moment we are quite in the dark in this matter as regards rabies, and the
dosage of patients is accordingly regulated solely by the apparent severity of their bites, and there
is no means of telling whether any particular man has had a sufficient quantity of the vaccine or
whether greater security might be attained by larger doses or a prolongation of the treatment.
It is possible that the deaths that occasionally occur in spite of the treatment might be pre-
vented by a higher dosage ; it is also possible that there is a certain number of persons who would.
never react properly whatever quantity of vaccine they might receive. Unfortunately with rabic
virus no exact experiments can be made as with easily isolated bacteria ; so the only possible
method seems to be to measure the antagonistic action of the serum of treated persons on an
• emulsion of virulent brain in vitro by inoculating animals subdurally with the mixture.
The method adopted was as follows. An emulsion of fresh fixed virus of a strength of 1 in 50,
made with salt solution in the usual way, was filtered through sterile filter paper to remove
the coarse particles. Preliminary gravimetric experiments had shown that filtration reduced the
strength of the emulsion by a variable amount, so that it was impossible to state with exactitude
the weight of brain substance actually suspended in the emulsion that was finally used. Starting
• with 1 in 50, the emulsion after filtration might be anything between I in 80 and 1 in 100.
The filtered emulsion was then mixed in sterile test tubes with measured quantities of the
serum on trial, incubated at 37° C for 1 hour, and thereafter injected. subdurally.
The time of contact and the temperature desirable had previously been determined by
sundry experiments. VVorking with an antirabic serum, which always destroyed the virulence of
fixed virus when mingled in the above described manner in the proportion of 20 volumes of serum
to 1 part by weight of fixed. virus brain in 1 hour at 37° C, it was found that :--
TABLE No. 2.
1 hour at 37' C was always sufficient for 20 serum to 1 fixed virus.
„
sometimes
,,
10
„
1
„
24 hours
„ quite„
„
1
„
5 minutes
„ not
20
„
1
„
5 minutes at l83° C was not sufficient for 20 serum to 1 virus.
1 hour
„
20
„
1 „
24 hours at 0º C.— 5' C was sufficient for 40 serum to 1 virus.
„ was not sufficient for 20 serum to 1 virus.
, 1
Our method is practically the same as that adopted by Marie (2), but this author speaks of
the action of antirabic serum on rabic emulsion as being nearly instantaneous, whereas
it appears from our experiments (Table 2) that contact of 24 hours will effect more than contact of
1 hour, and. , 1 hour more than 5 minutes. Temperature too is seen to have a decided
influence, a destruction being wrought at 37° C in 1 hour which was not accomplished at 18 . 3° C
in 1 hour or at 5° C in 24 hours.
As a matter of convenience we have relied on a contact of 1 hour at 37° C to suffice for all.
practical purposes, but it is clear when. the sources of experimental. errors are enumerated., namely,
uncertain variations in the virulence of the virus used, unavoidable variations in the strength of
- the emulsion used and unknown variations in the susceptibility of the animals employed as
evidence, that it would be unwise to anticipate exactly equivalent results from any one serum in.
distinct series of experiments.
Having first ascertained that the serum of normal men does not destroy fixed virus in the
proportion of 200 serum to 1. virus we proceeded to test whether any antirabic properties are
.developed in the blood of patients during their course of antirabic treatment. For this purpose
10 cc of blood were withdrawn by syringe from the median basilic vein, and the exuded serum wag
used 24 hours later for mixing with fixed. virus emulsion in different proportions, as previously
described.
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