MAMMALIA 243 



or infected ports, must be fumigated either at the end of each voyage 

 or at certain intervals. At most ports, also, the law requires certain 

 or all vessels to guard all lines leading to shore with metal rat-shields, 

 Fig. 155, to prevent rats from leaving or entering the vessels. While 

 rats are excellent swimmers they are not apt to deliberately jump into 

 the water and swim ashore. 



For killing rats in their burrows in fields, along streams, etc., carbon 

 disulphid is often very effective. A wad of cotton or any other ab- 

 sorbent substance is saturated and dropped into the hole, which is 

 then closed with dirt to prevent the escape of the gas; the rats are left 

 buried in the ground. 



Various so-called rat viruses are on the market that are supposed to 

 cause contagious bacterial diseases among rats. The idea is excellent 

 but so far none of these viruses, according to the Biological Survey, 

 has proved satisfactory. 



A number of domestic animals are commonly used to destroy rats, 

 the domestic cat being the most familiar. While an occasional cat is 

 found that is a veritable terror to rats, and many produce dealers and 

 others claim great efficiency for their cats, yet their value as ratters is 

 probably greatly exaggerated; a well- trained fox terrier or some other 

 breed of dog is usually worth many cats, as a destroyer of rats. Ferrets 

 were formerly much used, especially in connection with dogs, to rid 

 houses of rats, but they require experienced handling and are not so 

 commonly used as formerly. 



The natural enemies of rats will be discussed in connection with 

 mice, upon which they feed even more than upon rats. As has been 

 said some of these wild animals are often blamed for the destruction 

 of poultry really due to rats. 



In order that any campaign against rats may be effective coopera- 

 tion among the members of a community must be had. If one person 

 wage war upon rats on his property they will swarm over to the neigh- 

 boring properties and the only way to get extensive results is to make 

 the campaign a community affair and continue it from year to year. 

 By interesting women's and farmer's clubs, boards of trade and other 

 civic societies much may be accomplished. By having the town, 

 county or state place a bounty of a few cents a head (or tail) upon rats 

 the interest of the small boy may be attracted; and if, in addition, a 

 cash prize for the greatest number of rats brought in during a certain 



