i8 



Rats and Mice 



mouth of the flea becomes contaminated and infested with plague 

 germs. In due course the plague-smitten rat dies, and its fleas 

 have to seek other hosts. If another rat presents itself, the fleas 

 collect on it. The ''hungry fleas " at once attempt to feed; they 

 bite and pump blood again and again, each time forcing con- 

 taminated blood back into the system of the new host. The 

 latter is speedily infected with plague ; and so the disease goes on 

 spreading in an ever-widening circle, and a great mortality ensues 

 among the rats. 



Eat fleas carrying plague germs do not, unfortunately, always 

 select another rat as the successor of their first host. They often 

 collect on other rodents, and they have been known to infect^ 

 horses, dogs, and pigs. But very often man himself is the new 

 host, and a single germ is sufficient to infect him with plague. 

 In man such an infection always takes the form of Bubonic 

 Plague. This is not contagious ; it can only be transmitted to 

 man by a direct blood infection, as by the bite of rat fleas. At a 

 later stage, however, plague becomes more virulent among 

 humanity ; it develops into Pneumonic Plague, which is highly 

 contagious. Unless checked, it now becomes epidemic and spreads 

 death on every hand among the unfortunate people attacked. 



Often the advent of plague among people is heralded by a 

 noticeable mortality among the rats ; but this is not invariably 

 the case, for men are sometimes attacked before the disease has 

 made any visible strides among the rat population. Plague is 

 quite frequently detected among the rats in British ports ; it is 

 constantly arriving in this country, and every year deaths from 

 it occur among the human inhabitants. In East Suffolk, between 

 the Orwell and the Stour, plague seems to be endemic among the 

 common rats ; several human deaths from pneumonic plague have 

 occurred at various localities there in recent years. These cases 

 have recurred after intervals of many months, and in spite of the 

 most active and careful preventive measures known to sanitary 

 science. They serve to show that plague, once firmly estab- 

 lished, is most difficult to eradicate, and to warn us of the fact 

 that we can afford to take no risks in this matter. 



Trichinosis. — Eats and mice are the principal agents con- 

 cerned in disseminating and perpetuating this disease. The cause 

 of trichinosis is a very remarkable parasitic worm. Trichina spiralis. 

 Large numbers (often millions) of immature Trichina are sometimes 

 found embedded and encysted, in calcareous envelopes, in the 



