THE PEST OF RATS 25 
parasite are the rat and the hog itself. Pork 
‘becomes trichinous, then, only when swine eat 
the flesh of infected rats or hogs. Country 
slaughter-houses, where rats are abundant and 
swine are fed on offal, are the chief sources of 
trichinous pork. ‘That the danger from this 
source has not been confined to the rural 
slaughtering-places alone, is shown by the: in- 
vestigation conducted by the Biological Survey 
in 1909 into the ‘‘rat-nuisance,’’ said to exist 
about the great packing-houses in Chicago and 
St. Louis. The older establishments were 
found to be infested with rats, causing a se- 
rious aggregate loss, and endangering both the 
health of the workmen and the wholesomeness 
of the product; but this state of things has 
been greatly improved, and new buildings are 
‘designed to be rat-proof. 
Rats creep through drains and step about 
in all sorts of filth; and to their feet and fur 
clings slime which may be loaded with germs 
of typhoid, diptheria and any other of the 
malignant list of diseases due to bacilli that 
develop in darkness and filth. Consequently 
