MAMMALS 309 



the gas may be introduced by means of a small hand pump 

 constructed for this purpose. 



The mice and rats constitute a large family of which the 

 house mice and rats, the various field mice, the wood-rat, 

 Neotoma pennsylvanica, and the muskrat, Fiber zibethicus, are 

 familiar representatives. The common brown rat, Mus decu- 

 manus, was introduced into this country from Europe about 

 1775, and has now nearly wholly supplanted the black rat, M. 

 ralttis, also a European species, introduced about 1544. Rats 

 are by far the worst of all the mammalian pests. The damage 

 that they do to foods and stored products the world over 

 amounts to hundreds of millions of dollars annually and, what 

 is far worse, they may carry, as we shall learn (page 375), the 

 germs of the dreaded bubonic plague and are thus a constant 

 menace. The fight against them has been carried on for ages 

 and still they continue to multiply and spread. Poison and 

 traps are more or less successful, the degree of success depend- 

 ing, in a large measure, on the skill of the one who is doing the 

 poisoning or the trapping and to a still greater extent on the 

 age or experience of the rats, the old, experienced fellows be- 

 coming very cunning. The modern methods of fighting the 

 rat are to cut off its food supply and to destroy, as far as possi- 

 ble, its breeding places. A liberal supply of food means many 

 litters of rats and many young in a litter. Scarcity of food will 

 reduce both, so if garbage cans are kept closed and feed bins 

 and cellars and store houses made rat proof, the rats will 

 either die or seek a more hospitable place. The great fight 

 carried on against the rats in San Francisco when this city 

 successfully fought the plague some years ago, shows what 

 can be done by united effort directed along these lines. In 

 that fight fully 1,000,000 rats were slain, 8,000,000 square 

 feet of concrete were used in rat-proofing, more than 100,000 

 new, covered garbage cans were installed, and all rubbish was 

 cleaned up in all parts of the city. It was the rat fighting 

 that stayed the disease. 



The muskrat, Fiber spp., is one of our largest rats, reaching a 

 length of twenty-one inches. It lives in the water, and makes 

 houses there much as do beavers, and is hunted for its fur. 



