287
population and especially the susceptible rat population of the
inhabited districts. The number of rats in any area is dependent
almost entirely upon the available food supply for these animals,
while the most obvious result of the human overcrowding has been
a marked increase in the amount of waste food, both in the houses
end in the yards and lanes adjacent thereto. Efforts have been
made to keep pace with this increase in the house-refuse by improv-
ed scavenging, but it is obvious that where houses are overcrowded
with human beings and their many belongings, the cleanliness of
the premises falls below the average and refuse of all sorts lies
concealed amongst the general lumber.
1
4. Hongkong possesses both the mus decumanus or drain rat and
'the mus rattue or house rat and it has been our experience since
Plague first started in Hongkong that the mus decumanus remains
Plague
infected practically throughout the year while the mus rat-
tus only shows Plague infection during the period corresponding to
the human epidemic viz. February to July. Thus during the present
year no Plague rate were discovered during January; 5 were found
in February, all of them decumanus; 7 in March, all decumamus; 77
in April of which 4 were rattus and 73 decumanus; 247 during May
of which 69 were rattus and 178 decumanus; 107 in June of which 32
were rattus end 75 decurénus; and 38 in July of which 8 were rattur
and 30 decumams. The monthly incidence of the human cases of
Plague was as follows:-
A
January
February
March
9
-
24
73
April
-317
May
760
June
498
July
144
5.
It follows therefore that while man can and does contract
Plague from the mis decumanus, principally in warehouses, workshops
basements, stables and outhouses generally, the bulk of the epidem-
io is due to the spread of infection to the house rat, and every
(2)