as Enemies of JMankiiid. 



21 



Similarly, foot-and-mouth disease and dysentery are now 

 known to be carried by rats. 



Finally, the Common Eat makes its way into the store-places 

 and kitchens of our houses and restaurants. Into these places, 

 besides contaminating our food with its own germ-laden dejecta 

 and parasites, it brings a wealth of indescribable filth from its 

 favourite haunts in the adjoining sewers and drains. At this point 

 one may leave the reader to his own reflections. 



THE POSSIBILITY OF THE EXTEEMINATION 

 OF EATS. 



Having thus described some of the evils resulting from the 

 presence of rats in Britain, we proceed next to consider the size of 

 the rat population, its natural increase, if any, and the prospect 

 and means of controlling it successfully in future. 



There have been many attempts to calculate the reproductive 

 potential of rats. For instance, F. von Fischer, in 1872, concluded 

 that the progeny of a single pair might in ten years amount to no 

 less than 48,319,698,843,030,344,720 individuals. Eucker, more 

 recently, has computed the increase of a pair in five years at 

 940,369,969,152 rats. 



Lantz was not so ambitious ; for the purposes of his calcula- 

 tion he assumed the rats to breed only three times a year, and 

 to have average litters of ten. Breeding at this rate uninterruptedly 

 for three years, producing sexes in equal numbers, and with no 

 deaths, the progeny of a single pair at the ninth generation w^ould 

 be 20,155,392 rats. 



Zuschlag assumed a pair to have six litters of eight in a year ; 

 that the young would breed when 3^ months old, then with equal 

 sexes and no deaths the progeny at the end of the first year would 

 be 880 rats. 



Although such calculations are purely theoretical, and although 

 their results, in ordinary circumstances, will never be approached 

 in Nature, they are not extravagant, qiia the power to reproduce, 

 but are based upon moderate and conservative estimates. In 

 proof we may cite Kolazy's record that two females kept by him 

 had twenty-six litters in a space of thirteen months, and produced 

 180 young — almost double the number assumed by Zuschlag. We 

 can, therefore, readily understand how the progeny of a few 

 rats introduced to a new country by a ship may, in favourable 



