150 Proceedings of the Royal Physical Society. 



to the discovery of many of the other Mammals as 

 visitors. 



Of the 115 birds, the greater number are found in No. 2, 

 and 74 in No. 3; of which 8 are rare and 4 are peculiar 

 to it. 



V. On the Gnawing of Water and Gas Pipes hy Rats and Mice. 

 By A. Galletly, Museum of Science and Art, Edinburgh. 



(Read 18th January 1882.) 



The incisor teeth of the rodentia are sharp, strong, and 

 chisel-like. They continue to grow during life, and through 

 the dentine, of which the body of the tooth is composed, 

 wearing away faster than the thin, hard, anterior layer of 

 enamel, the latter forms a sharp cutting edge, strengthened 

 by a bevelled backing of dentine. The condyles of the lower 

 jaw are antero-posteriorly elongated, so as to allow of a con- 

 siderable amount of back and forward motion on the cranium, 

 or vice versa, if the latter be fixed, of the cranium upon the 

 lower jaw. By this peculiarity in the anatomy of its head, 

 a rodent can at will bring the upper incisors in front of the 

 lower, or the lower in front of the upper, and thus, by an 

 equal wearing away of both pairs of incisors, their chisel 

 shape is maintained. If a rat or a rabbit, for example, breaks 

 an incisor tooth, or if through any other cause this equal 

 wearing of any of the front teeth is interfered with, then a 

 curious result follows. The tooth which has no longer an 

 opposite one to rub against grows long and circular, and 

 eventually prevents the animal from taking food. 



With these few words of explanation about the nature of 

 its teeth, I shall now take up the rat's doings in the way of 

 destroying water-pipes. According to some authorities, the 

 rat in ancient Egypt symbolised "utter destruction," and 

 also "judgment," because it always chooses the best bread 

 for its repast. Perhaps these animals likewise choose the 

 best water for their drink, and this may sometimes be the 

 reason why, as some persons assert, they gnaw holes into 



