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In places where rats are very numerous plague may develop when

climatic conditions are adverse, i.e., when rat-fleas are scarce, but

plague tends to disappear with the advent of hot dry weather.

It cannot be too strongly emphasized that anti-rat measures, directed

towards the eradication of plague infection, can be prosecuted with

most chance of success in the hot dry months when plague cases and

foci of infection are fewest. The relatively plague-free season should

synchronize with maximum anti-plague effort and not be regarded as a

suitable time for a cessation of anti-plague measures.

Anti-plague measures can be grouped under four heads:-

(a) Rat elimination or the prevention of rat infestation. This

comprises such modifications in the habits, customs, and dwellings of

a community as will result in a diminished rat infestation in the homes

of the people and make the association between rats and men less

intimate than at present.

(b) Measures designed to protect the rat population of any given

town or village from plague infection. These entail a clear under-

standing of the manner in which plague infection is carried from

place to place.

(c) Rat destruction designed, as is (a), to diminish the chances

of infection, and to keep the rat population at so low a level that is

plague be introduced the severity of the resulting epidemic will be

appreciably diminished.

(d) If our efforts under these three heads fail to keep plague out

it is left to try and render the human population immune to attacks

of the disease by means of inoculation, or to remove the population

at risk from close association with infected rats. The latter involves

the evacuation of infected dwellings and the provision of temporary

accommodation outside the rat-infested, plague-infected area.

Measures included under (a), (b) and (c) can be carried out at any

season of the year; measures under (d) are generally applicable only

in the plague season.

Segregation of the sick is not essential. For all practical purposes

the patient suffering from bubonic plague is not capable of infecting

those in close attendance on him. Such a statement is not true of

pneumonic plague. Small outbreaks of this disease, which is extremely

infectious, are occasionally experienced in India. These are, however,

of infrequent occurrence and of small moment when compared with

the incidence of bubonic plague.

It will be noted that of the four 'components' of a plague

epidemic, viz., the plague bacillus, the rat-flea, the rat, and man, only

the rat and man have been specifically mentioned in this preliminary

discussion of preventive measures. The plague bacillus is so short-

lived outside the body of either the rat-flea, the rat, or man, that

for practical purposes it need not be considered as possessing an

independent existence. Similarly, the welfare of the rat-flea is so

dependent on the plentiful supply of rats which they parasitize, and

has so short a life apart from its proper host, especially if it be infected

with plague, that 'anti-flea' measures received no specific mention.

Such measures will be referred to when (b) is under detailed consi-

deration: they have very decided value and should in no wise be

overlooked.