THE RECOIL OF MAN'S INFLUENCE 507 



habits is a menace to human life, since it contaminates, with 

 bacteria carried on its feet, food and drink set aside for 

 human use. Thus it has been found to spread cholera, 

 typhoid fever, and tropical dysentery ; and a relation, more 

 than suspicious, which has been traced between the numbers 

 of Flies and of human deaths in Manchester, suggests that 

 the House Fly is closely connected with the epidemics of 

 summer or infantile diarrhoea, which in some towns sweep 

 away so many children's lives. It seems obvious too that 

 the Fly may readily help in the dispersal of the "germs" of 

 such diseases as tuberculosis, anthrax, smallpox, ophthalmia 

 and infantile paralysis. 



RATS AND DISEASE 



Rats have spread vastly under the influence of man. 

 Not only have they been introduced to new countries in 

 ships, the ancestors of the whole stock of rats in Britain 

 were voyagers brought from across seas, but in most 

 countries, the increase of offal and of garbage in general, 

 and the development of sewer systems which afford food 

 in abundance and perfect security, have multiplied the 

 numbers of rats beyond belief. This effect of man's civili- 

 zation results in direct damage to his goods and stored food 

 and buildings, but it is of more account on other grounds. 

 Rats and the Black Rat and the Brown or Norway Rat 

 are almost equally guilty nourish undesired colleagues 

 in the many species of Fleas which infest them, and these 

 two allies, rats and rat-fleas, have been responsible for the 

 deaths of upwards of 7,000,000 people in the course of 

 fifteen years (1896-1911) in India alone. 



It has been conclusively shown that bubonic plague in 

 man depends entirely upon the disease in the rat, and that 

 the disease is conveyed from one rat to another and from 

 the rat to man solely by one or other of the rat-fleas. Up 

 to the present time eight species of rat-fleas have been shown 

 to be capable of transmitting plague, and of these five are 

 common British species, while the chief sinner, the eastern 

 Plague Y\tdi(Xenopsylla cheopsis], is occasionally brought from 

 abroad to our seaports. 



There is no need to recall how in past days epi- 

 demics of plague flew like messengers of death across the 



