Published online by Cambridge University Press: 15 May 2009
1. Both in Bombay city and in the Amritsar district of the Punjab there is a distinct seasonal variation in the number of rat fleas.
2. In these places this seasonal variation of rat fleas corresponds directly in a general way with the plague mortality. During the season when plague is epidemic the average number of fleas per rat is above the mean, while during the non-epidemic season it is below the mean. The height of the epidemic corresponds fairly closely with the season of maximum flea prevalence.
page 267 note 1 The method on which this and all subsequent curves are constructed was as follows. The bimonthly plague mortality for the period over which the curve extends was taken, and a mean of these figures calculated. Then the percentage above or below this mean for each bimonthly figure was determined and the curve constructed on these percentages. In this way the relative severity of the different epidemics in the same place can be seen at a glance.
page 287 note 1 It must be remembered in this connection that the absence of a well-marked septicaemia post mortem may be the result of the low temperature inhibiting multiplication of bacilli in the blood of the rat after death.