1 54 Proceedings of the Boyal Tliysical Society. 



Since mice are greatly more common in houses tlian rats, 

 and both gnaw metal tubing, it follows that the smaller and 

 usually less dreaded species is likely to be, of the two, by far 

 the more frequent cause of injury to gas-pipes. Few of us ever 

 consider the risk we are exposed to by the doings of these 

 insignificant looking creatures. We all know that they gnaw 

 books, title-deeds, and the like, but comparatively few of us 

 are aware how easily they can prepare an explosive mixture 

 by which at any moment we may be blown up. Very likely 

 many of the unaccountable gas explosions we hear of are due 

 to rats or mice. 



Internal gas-pipes are usually made either of tin or of 

 what is called " composition metal," which is an alloy con- 

 taining very little of anything but lead. Tin pipe is decidedly 

 the harder and better of the two kinds, and was long in use 

 before the demand for cheap gasfittings caused composition 

 pipe to be made. Eats can easily cut both kinds with their 

 teeth, but mice apparently can only gnaw tin pipe with con- 

 siderable trouble, as they seldom try it, but with the softer 

 gas tubing they have no difficulty. As an example of what 

 a single mouse can do in the way of gnawing, I may state, 

 that, having unconsciously locked one inside a cabinet 

 with close-fitting doors, the poor animal, in its struggle to 

 escape, had splayed away with its teeth the square edge of 

 a hard mahogany shelf to the extent of fully an eighth of an 

 inch for about two feet of its length. 



I have here three pieces of composition gas-pipe, removed 

 very recently from a large establishment on the North Bridge, 

 Edinburgh, by Messrs Stewart & Eae, Eegister Street, whose 

 manager, Mr Thorburn, has kindly preserved them for me. 

 This was the second time that mice-gnawed pipes were taken 

 away from under the floor of the dining-hall on the same 

 premises. The specimens illustrate very well the usual appear- 

 ance of pipes so injured, and the position they were taken from 

 was one where mice commonly attack gas tubing in order to 

 make a passage for themselves. The pipe from which these 

 gnawed pieces were cut was laid across the joists in the narrow 

 space between the flooring boards and the " deafening." It 

 was passed through a notch in each joist, and it was at these 



