THE MOUSE AND ITS ALLIES 319 



Asia, it crossed the Volga in great troops in 1727, occupied 

 Russia in 1730, France in 1750, and Denmark about 1810. 

 Before the advance of this powerful and aggressive foe, 

 the black rat of Europe gave way, and became well-nigh 

 exterminated, although of late it is said to be reasserting 

 itself in Germany. The brown rat was introduced into 

 America in 1775, has spread over the whole country, 

 reaching the Paciiic coast about 1855, and, as in Europe, 

 has nearly exterminated the black rat. 



The habits of rats and mice are well known. They 

 inhabit our buildings, gnaw our doors and furniture, de- 

 stroy our provisions, kill poultry, and aid in spreading 

 disease. They shun the light, living in holes during the 

 day, run with great agility, and are capable of making 

 long leaps. Owing to their instinct to go into holes, they 

 are easily trapped by a funnel-shaped opening leading into 

 a closed box. Despite the ease of trapping and their 

 destruction by cats, they maintain themselves by virtue of 

 a great fecundity, for, if no deaths occur, several hundred 

 young may, in one year, descend from a single pair. 



The food of mice is very varied. They naturally thrive 

 best on a vegetable diet; oats especially are recommended 

 for tame mice, and hard-shelled nuts are useful because 

 the mice keep their teeth sharp by gnawing the shells. If 

 the teeth are not kept worn off they soon become incon- 

 veniently long owing to the fact that they grow continu- 

 ously throughout life, and are not formed, once for all, like 

 our teeth. In addition to plant materials, rats and mice 

 eat a certain amount of animal food. 



The different races of tame mice illustrate the results 

 obtained by preserving sports and selecting the best for 

 breeding purposes. The white mouse, for instance, is an 



