1901-2.] Plague Research Laboratory of Government of India. 143 
that a measure which reduces the mortality in a plague-stricken 
community from an average of 73*3 per cent, to 57*3 in those develop- 
ing plague the very day after inoculation, is one which acts with 
astonishing rapidity. On this point Haffkine, in his evidence before 
the Indian Plague Commission, says : * “ The time necessary for the 
plague prophylactic to produce a useful effect is shorter than in any 
preventive treatment known, this period being in the anti-cholera 
inoculation four days, in vaccination against small-pox seven days, 
in the inoculation against anthrax twelve days, in the inoculation 
against rabies fifteen days, and in the present treatment apparently 
less than twenty -four hours.” In the case of Undhera village, 
already given, we have seen f that the number of attacks among the 
inoculated at once becomes less than among those not so operated 
on. As the villagers were divided into two groups as evenly as 
possible, there is no reason to suppose that there could have been 
fewer persons in the incubation stage of plague among those 
inoculated than among their uninoculated relatives. Why, then, 
did they have but two cases in the first week instead of eleven, 
which is the number they ought to have had if they had suffered 
in the same proportion as the uninoculated ? The answer plainly is, 
that the inoculation had aborted the disease in these cases. 
Further, if we study the figures in the last column of the table, 
we see that there is really very little difference from day to day 
in the effect produced during the first ten days after inoculation, 
although there is a steady increase of effect observable as time 
goes on. Up to the ten-day limit the case-mortality is 48*04 
per cent., while after this period it is 40*6 per cent. These daily 
variations, and the comparatively small difference in the rates 
between the beginning and the end of the ten-day period, seem 
do point to a sudden very considerable measure of protection 
being secured after the lapse of twenty-four hours only. The reply 
to the first part of the query is therefore : — Protection begins to 
be effective after the lapse of twenty-four hours, and goes on 
slowly and steadily increasing for some considerable number of 
days thereafter. It is proper, however, to point out that the 
Indian Plague Commission, from a consideration of the case-mortality 
* Report of Indian Plague Commission , vol. i. p. 6, para. 47. 
t Supra, p. 132. 
