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. 



