The history of the study by modern methods of the epidemiology of plague may be said to date from the discovery of B. pestis by Yersin and Kitasato in 1894. The severe outbreaks which since then have yearly recurred, notably in Bombay and Hongkong, have offered a wide field for investigation. That the opportunities thus afforded have not been neglected is sufficiently shown in the statement that in Bombay alone no fewer than six scientific commissions devoted their attention to various aspects of the disease within a few years. In addition, epidemics have been investigated in many places throughout the world.

One of the first duties which the present Commission had to undertake was to decide where the epidemiological observations which were necessary to be made should be carried out. After various parts had been visited, it was decided that the headquarters of the Commission should be in Bombay, and that Bombay City and Island should, in the first instance at least, be put under observation for epidemiological purposes.

(1) Worli village is badly infested with rats, practically all M. rattus.

(2) Persistent trapping for one year appeared to reduce the rat population to approximately one quarter of the original number.

(3) Three cases of plague which occurred in the village were investigated. It is probable that these three cases all contracted the infection outside the village.

(4) In two instances there is evidence which points to infection having been introduced in the clothing or persons of people, and of this spreading in one instance to a guinea-pig, and in the other instance to rats.

(1) The question of the alleged spread of infection by direct contact with a suffering case has been discussed. Our observations in a plague hospital and with material obtained from this hospital lead us to conclude that such a mode of spread does not exist. Support is given to this view by a consideration of the influence of imported cases on the spread of the epidemic and by an investigation of the relative frequency of single and multiple cases in houses and buildings. We have, further, referred to our experience that a rat epizootic is alone sufficient to account for a widespread dissemination of infection throughout a locality. A review of the whole of the evidence on this point brings us to the conclusion that contact with plague cases plays no part in the spread of the epidemic.

(2) In discussing the question of the infectivity of houses, evidence has been brought forward which points to the rat flea being the transmitting agent of infection from rat to man. Further, reasons have been given for the view that plague does not persist in a locality apart from infection amongst the rats.

(3) From arguments brought forward in the discussion of the two previous questions we conclude that the epidemic is wholly dependent upon the epizootics.

(4) It has been shown that infection may be transported to a distance by means of rat fleas in clothing or merchandise and that such infection, when imported into a hitherto uninfected locality, may give rise to an epizootic in the rats.

(5) Our observations lead us to conclude that plague in domestic animals in Bombay either does not occur or occurs so seldom that it cannot be said to possess any significance from an epidemiological standpoint.

The villages selected for the present series of observations were Dhand and Kasel in the Arnritsar District of the Punjab. They are situated about 10 miles south-west of Amritsar City and within a distance of ¾ mile of each other. They are typical Punjab villages of about 2,000 and 4,000 inhabitants respectively.

Volume VII. p. 470, lines 6 and 34. For “in the Punjab” read “in the Punjab villages of Dhand and Kasel.” In some parts of the Punjab acute human plague occurs in the oflf-plague season.

Case Q, in the same house as case T, in the northern part of Dhand, is marked R in Map 1: it appears as “4” in Map 12. The real case R is in the same house as W on Map 1.