2 CIVIC BIOLOGY 



As an illustration, take the case of the common rat. These 

 animals are probably costing the country $500,000,000 annu- 

 ally in spread of disease, in damage to buildings, merchandise, 

 and produce, and in cost of traps, poisons, and labor; and 

 since bubonic plague has gained a foothold in America, they 

 positively must be exterminated. A single pair may breed 



FIG. 1. Rats, where they all belong 



1250 rats in a year. As we are now doing, Smith attempts to 

 rid his premises of the pests in October, driving many of them 

 over to Jones. Jones undertakes the work in November, driv- 

 ing them back to Smith, and in December both are practically 

 where they were before. The same amount of effort, properly 

 coordinated, might have proved effective. This principle ap- 

 plies with added force to larger groups, and it is quite possi- 

 ble that with even less expense and labor than is now almost 



