THE PEST OF RATS 19 
Rats as carriers of disease. Finally, rats are 
always a menace to health, and may become 
the agents of the dissemination of the most 
dreadful and virulent of diseases—the Asiatic 
plague, which has more than once decimated 
the civilized world. It has been calculated that 
25,000,000 of persons perished in an epidemic 
of this character which swept over the world 
in the 14th century; and it did not require the 
literary genius of a De Foe to perpetuate the 
memory of the awful visitation which almost 
depopulated London and set all Europe in 
mourning toward the end of the 16th century. 
Even then, in the cloud of mystery, supersti- 
tion and horror of fear which made most men 
blind and helpless, the truth was dimly recog- 
nized by a few,—namely that it was not the 
wrath of God nor the malignancy of some evil 
spirit nor a miasm from earth or sea that 
struck men down, but the communication of 
disease from the sick to the well. This, it was 
observed, could be effected not only by contact 
with human victims, but that the contagion was 
caught and passed on by all the small animals 
about a house. Hence orders were issued that 
