as Enemies of Mankind, 



might expect the birth of 12,000,000 pairs possessing a chance of 

 breeding. Further, although it would considerably affect the 

 calculations if they were extended to cover the year 1919, the 

 assumption of three instead of six litters would make comparatively 

 little difference to the figures given for 1918 ; our 10,000,000 pairs 

 of Jan. 1 might still grow to 32,000,000 by Dec. 31 ; the cost of 

 keeping them, estimated at £9,224,500 with six litters, would only 

 be reduced by £232,500 if we assumed the birth of the first three 

 litters only. 



Such a calculation, although open, it is true, to many objections, 

 suffices to prove that we are dealing with a very formidable 

 problem indeed. Such a rate of increase must very soon lead 

 to disaster if it be not checked ; it cannot continue. In normal 

 conditions Nature would and does step in to check it. The 

 natural enemies of the rat— carnivorous mammals, such as weasels, 

 stoats, polecats, martens, cats, and foxes ; birds of prey like owls 

 and kestrels ; reptiles such as snakes — these, with their food- 

 supply so greatly increased, would multiply in proportion. If, in 

 spite of the havoc wrought by these carnivorous creatures, the 

 numbers of rats continued to increase unduly. Nature's other and 

 more dreadful remedy would assert itself. Food and space are 

 limited ; underfeeding and overcrowding would sap the vitality of 

 the rats ; the weaker individuals would be attacked by micro- 

 organisms. Bacillus loestis, and innumerable others ; their stronger 

 brethren would in turn become infected, either by devouring the 

 bodies of, or by receiving parasites from those that succumbed. 

 Pestilence would break out in this way among the rats all over the 

 country, and it w^ould in a very short time reduce their numbers 

 to insignificance. 



So much for normal conditions. One of the* penalties of civili- 

 zation is that we deprive ourselves of the assistance of most of our 

 carnivorous allies. Polecats and martens have practically gone^ 

 and wild cats with them ; domestic cats as a class are not keen 

 on ratting, though there are exceptions ; foxes are too mischievous 

 to poultry, and their numbers are strictly limited; weasels and stoats, 

 which do an invaluable service in killing large numbers of young 

 rats (and it should be recognized that young rats are always more 

 numerous and potentially more dangerous than adults) are every- 

 where persecuted ; owls and kestrels are too frequently shot at sight ; 

 and snakes no longer count. We have, it is true, our domestic dogs 

 and ferrets. Working with an experienced man, these do a great 



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