Fleas and Plague 151 



killed by it in great numbers. An outbreak of 

 plague among men is often preceded by a very 

 noticeable outbreak among rats. 



Rats dying of the plague have their blood filled 

 with the plague bacillus. Fleas or other suctorial 

 insects feeding on such rats take myriads of these 

 bacilli into their stomach and get many on their 

 proboscis. 



The fleas usually leave a rat as soon as it dies 

 and of course seek some other source of food. 

 When such infected fleas are permitted to bite other 

 rats or guinea-pigs these animals often develop the 

 disease. Several of the species of fleas that infest 

 rats will bite man also, and in the cases of many 

 plague patients it can be definitely shown that they 

 had recently been bitten by fleas. 



STRUCTURE AND HABITS OF FLEAS 



A study of the structure and habits of fleas shows 

 that in many respects they are particularly adapted 

 for spreading such a disease as bubonic plague. 

 The piercing proboscis consists of three long needle- 

 like organs, the epipharynx and mandibles, and a 

 lower lip or labium. The mandibles have the sides 

 serrate like a two-edged saw. The labium is di- 

 vided close to its base so that it really consists of 

 two slender four-segmented organs which lie close 



