158 INSECTS AND MAN 



"the god whose arrows spread the plague," and, at the 

 same time, as " the destroyer of rats." On monuments this 

 divinity was represented treading on a rat. Again, Dr 

 Samboii, an authority on the history of plague, has de- 

 scribed to the writer a coin of Lucius Verus, struck at 

 Pergamum during an epidemic of plague. It represents 

 Esculapius, the god of medicine, with a rat at his feet, and 

 near by is a small naked figure with arms outstretched, in 

 an attitude of fear or worship. Defoe, writing of the great 

 plague, said : " All possible endeavours were used to destroy 

 the mice and rats, especially the latter, by laying ratsbane 

 and other poisons for them, and a prodigious multitude of 

 them were also destroyed." 



We now have absolute proof that when an epidemic of 

 plague breaks out, it first of all spreads from rat to rat 

 and then from rats to man. Coastal towns are the first 

 affected, and those who have had dealings with a ship 

 from an infected port are usually the first attacked. 

 Whilst rats are the chief source of plague, mice, cats, 

 squirrels, monkeys, and other animals may also become 

 vehicles of infection. 



The plague flea, that is to say the flea most usually 

 associated with the transmission of the disease, is known 

 as Xenopsylla cheopsis (fig. 44) ; it is sometimes called the 

 Oriental rat flea. Its original home is the Nile valley, but 

 it has now been distributed all over the warmer parts of 

 the world by rats ; it cannot, however, stand cold weather. 

 In colour it is lighter and in size smaller than the human 

 flea, Pulex irritans, which, by the way, is also capable of 

 spreading plague, as is the European rat flea, Geratophyllus 

 fasciatus, and the Californian ground-squirrel flea, Hoplo- 

 psyllus anomalus. When a rat or other host infected with 

 plague dies, its fleas abandon its carcass and seek some 

 other warm-blooded animal. Often these insects literally 

 swarm during plague epidemics, and, at Sydney, during an 

 outbreak, the labourers on the wharves used to tie strings 



