( n ) 
At Singapore and Penang there are launches 
fitted with apparatus for the Clayton disinfection of 
ships. 
Zymotic or Infectious Diseases. 
Plague. 
Plague in a mild form is endemic among the 
rats- From time to time, for reasons unknown, the 
virulence of the causative organism becomes enhanced 
and an epizootic spreads among the rodents. When 
this happens isolated cases of human disease occur, 
but there is little tendency to spread and up to date 
there never has been an epidemic. The immunity of 
humans is ascribed to the consistently high atmos- 
pheric temperature which is detrimental to flea 
propagation. The common Malayan house rat is 
Mws grisieventer and the flea it carries is Xenopsylla 
Cheopis. 
Cholera. 
Though there have been epidemics of the disease, 
Malaya cannot be called a cholera country. The reason 
for the immunity is the rainfall which being normally 
evenly distributed and adequate in quantity provides 
tolerable drinking water supplies for the majority. 
Occasionally, in certain parts of the alluvial plains 
during periods of drought, outbreaks occur. Formerly 
these outbreaks were more common but the provision 
of public water supplies in towns and villages has had 
very beneficial results. For some years there have 
been few cases and no epidemics in the Federated 
Malay States or the Straits Settlements. 
