RATS AND MICE 79 



from the rest as rodent or gnawing animals, by the struc- 

 ture and arrangement of their teeth. In a rodent the 

 incisors or front teeth are long and chisel-edged, grow 

 perpetually at the base, and are separated by a wide 

 interval from the teeth next behind, which are always 

 grinders, the canines or eye-teeth being undeveloped. 

 Rats and mice are rodents, but the shrew, though popu- 

 larly called a field-mouse, is not a mouse, nor even a rodent. 

 The shrew has incisors, which are not greatly prolonged, 

 and do not continue to grow at the base ; canine teeth 

 are present, and there is no conspicuous gap between the 

 incisors and the grinders. Rats, mice, voles, squirrels, 

 rabbits, and guinea-pigs are familiar examples of the 

 rodent order. Rats and mice, differing in this from all 

 other common European rodents, have long bare tails, 

 with rings of overlapping scales. The voles, which are 

 often called by such names as field-mouse or water-rat, 

 have short hairy tails. 



It is only in comparatively modern times that mankind 

 has dwelt in houses constructed so as to give facilities 

 for the parasitic life of rats and mice. During the middle 

 ages an Englishman's house was one-storied, and had no 

 floor but hard- trodden earth. There were no ceilings 

 with floors above, no wainscots, no holes for water-pipes, 

 no drains ; and it is easy to understand that there were 

 then no house-rats, while mice were chiefly found in barns. 

 As houses became more elaborate, and trade between 

 distant countries frequent, three sorts of rats and mice 

 came to abound in our houses, and all three have now 

 spread to distant parts of the earth. They came to us 

 from the far east, India or China. The domestic mouse 

 came first, though little is known as to the time and manner 

 of its coming. Even so late as the twelfth century we 

 had no rats, and it is said that there is no ancient name 

 for a rat in any European language. The first rat to 

 enter Western Europe was the black rat, a species of small 

 size, only 7 or 7! inches long, of iron-grey colour, paler 



