THE PEST OF RATS 23 
rat-flea will bite and communicate the disease 
from rat to rat, and an outbreak of plague 
among men is usually preceded by an epidemic 
among the rats. The rat-flea does not bite 
man; but those which live on human beings 
will thrive on rats and may return from an in- 
fected rat to a human host if opportunity offers. 
The fleas of dogs and cats will temporarily live 
on the skin of both rodents and human beings, 
and may thus take a part in the transmission 
of plague. The fleas usually leave a rat or 
other animal as soon as it dies, and, with their 
stomachs full of plague-bacilli, with others 
clinging to their proboscis and sucking lips, 
they seek new hosts. The new host, whether 
rat, or some other animal, or perchance a 
human being, is soon bitten with these infected 
mouths, and thus receives the germs of the 
malady. . 
Those who wish to pursue the study of this 
matter in further detail will find a very full 
exposition of it, and of the general relations of 
insects to common diseases, in R. W. Doane’s 
Insects and Disease. (New York, Holt, 1910). 
