MAMMALIA 



393 



The genus Rattus includes a number of species, all of which are 

 important as disease carriers. (Figure 222.) 



The brown rats (R. norvegicus) destroy grains, poultry and nesting 

 birds, carry away eggs, sometimes cause fires, and even bite through 

 lead pipes and cause floods. The black rat of England was the 

 carrier of the " great plague " 

 of 1665 which destroyed one 

 hundred thousand people. 

 Brown rats eventually drove 

 the black rat out of England. 

 It is now chiefly confined to 

 ships. It disseminates bu- 

 bonic plague, which is trans- 

 mitted by rat -fleas to ground 

 squirrels. Ships in port have 

 three-foot metal discs guard- 

 ing their hawsers. Poison 

 baits and fumigants are used 

 to destroy rats in ships and 

 storehouses that are not rat- 

 proofed. 



The Eastern wood rat 

 (pack rat, trade rat), the 

 most handsome of the rats, is 

 noted for its mental capacity. 

 It stores food, but also steals 

 tools, silverware and even 

 watches, and stores them 

 away. Vernon Bailey states 

 that they are edible, " better 

 than Gray Squirrels." 



The albino rat is our most 

 important mammal for ex- 

 perimental purposes, and has 

 been inbred for nutrition and 

 other studies (see p. 441). 



The common house mouse 

 {Mus musculus), a species introduced from Europe, is an important 

 enemy of food stuffs and especially injurious in warehouses. The 

 field mouse or meadow mouse (see Figure 223) is a short-eared, 



Fig. 222. Brown rat infested by Cysti- 

 cercus fasciolaris. (A. T. Hopwood, Para- 

 sitology, vol. 14, no. I.) 



