152 ANIMAL COMPETITORS 
and southern California (Clitellus beecheyi) 
has special prominence in our list because it 
shares with the rat the bad distinction of being 
a dangerous carrier of plague-germs. It was 
observed as early as 1903, as we learn from Pro- 
fessor Doane’s book previously alluded to, that 
an epidemic was killing these ground-squirrels 
in the neighborhood of San Francisco bay. 
The matter was at once investigated by Dr. Ru- 
pert. Blue, of the U. S. Public Health and 
Marine Hospital Service, who speedily ascer- 
tained that the disease was bubonic plague, 
which had probably been caught from the town 
rats: which at harvest time wander into the 
country in large numbers and make free use of 
the holes and runways of the field-squirrels. 
A single infected rat might sow the seeds, for 
its fleas, escaping, from its dead body, would 
readily attach themselves to a squirrel and 
multiply and spread among them. Among the 
tens of thousands killed and examined a con- 
siderable number of infected ones have been 
found; and several instances are recorded in 
which human cases of plague in, California 
resulted from handling infected squirrels. 
