as Enemies of Mankind. 



15 



The second case is that of Lesser Cumbrae, an island of 900 acres 

 in the Firth of Clyde. According to Boelter (quoting from 

 Chambers' Journal) rats had been known on the island for a 

 number of years, but they seem to have given no particular 

 trouble. Then a French ship was wrecked and its rats made their 

 way to the shore ; they multiplied at a tremendous rate, and in the 

 course of four years developed into a serious plague. In 1907 the 

 keeper lost five tons of turnips ; at Christmas the rats attacked, 

 killed and devoured a 201b. turkey. The rabbits, rose bushes, wild 

 duck, mangolds and woodcock inhabiting the island were 

 threatened with extermination. At last virus was used (this time 

 with success, be it noted) and the rats succumbed. 



Various estimates of the value of the damage caused by rats to 

 property and materials in Britain and other countries have been 

 published. Quite apart from the diflficulty or impossibility of 

 obtaining accurate information as to the number of rats inhabiting 

 any given country, it is most difficult to estimate the loss. On the 

 one hand, although rats consume and spoil vast quantities of food 

 and materials, both in course of production and in store, they also 

 eat much matter which is purely waste. And further, while in 

 some cases the damage done is promptly detected and recognized 

 as being due to rats, and the loss occasioned has a definite 

 measure, in the majority the damage is done unobtrusively and 

 silently to things which are developing and of which the value has 

 not been ascertained. The loss is often gradual and not easily 

 detected (as when food is stolen from the supplies of domestic 

 animals) ; but it is continuous and soon totals up to a large sum. 



To the actual damage caused by rats we have to add the large 

 sums which are annually expended by public bodies, companies, 

 and private individuals on rat-catching operations. According to 

 Boelter, the capital employed in this country in providing rat- 

 catching or rat-killing apparatus had grown to £2,000,000 in 1909. 



Boelter assumed the rat population of Great Britain to be 

 40,000,000 — i.e., about one to each acre cultivated, or one per head 

 of the human population. He further assumed that each rat on 

 an average occasioned a daily loss of one farthing ; on these 

 assumptions, the total annual damage done by rats in this country 

 amounts to £15,000,000. This estimate does not take into account 

 the damage done by rats on our ships ; it relates solely to the rural 

 and urban activities of these animals. The estimate received the 

 approval of Sir J. Crichton-Browne, and enquiries made of a very 



