INSECTS AS AGENTS IN SPREAD OF DISEASE 539 



suffering from typhoid fever, or to those of a chronic carrier of this 

 disease, they may deposit the virulent bacteria upon food that later 

 finds its way into our own bodies. Bacillary dysentery may be spread 

 in the same fashion as well as many other gastro-enteric infections. 



The house fly occurs practically throughout the entire civilized 

 world and under all conditions is a continual menace to public health. 

 In rural communities, however, where the proper disposal of waste 

 matter of all kinds is most difficult, the importance of these insects is 

 correspondingly increased. 



The house fly is not the only insect which may act as a carrier of 

 typhoid, for Dutton has shown experimentally that this may be spread 

 by the bed-bug. These insects become infected through feeding on the 

 blood of a person in the acute stage of the disease and for at least 

 twenty-four hours retain the bacteria in a sufficiently virulent condi- 

 tion to inoculate a second person whom they may bite. That other 

 biting insects such as fleas and mosquitoes may act in the same way is 

 as yet unproved, but is by no means improbable. 



Several other species of flies appear regularly in houses, but in far 

 lesser numbers, and none exhibit to such a marked degree the peculiar 

 tastes of the house fly, which wanders back and forth from filth to food, 

 feeding on each in turn. In this method of feeding lies the danger of 

 infection by house flies ; they are equally fond of clean and filthy mate- 

 rials, and their frequent migrations from one to the other multiply their 

 opportunities to pick up pathogenic organisms that may be later de- 

 posited upon foods. 



The flea is another domestic insect which was looked upon only as a 

 nuisance until it was shown that certain kinds of fleas are agents in 

 spreading bubonic plague. The most terrible epidemics of which we 

 have any historical record have been those of plague, or "black death." 

 One swept from Egypt in the sixth century before the Christian era and 

 invaded Europe and Asia, where it raged for sixty years. A similar one 

 spread through the whole known world in the fourteenth century and 

 is thought to have caused over twenty-five million deaths before it 

 subsided. 



In 1898 Simond suspected fleas as agents in the spread of plague 

 and his suspicions have since been fully justified by Verjbitski and 

 others. Plague is common to rats, certain other rodents and man, and 

 is usually carried to man by the bites of fleas which have become 

 infected from plague-stricken rats. The flea most commonly concerned 

 is the rat flea, Lcernopsylla cheopis. The transfer of plague bacteria is 

 mechanical in nature, and other fleas, bed-bugs, etc., may also act as 

 carriers, although far less commonly. 



The plague bacilli (Bacillus pestis) appear only in fleas and bugs 

 which have bitten affected persons or rats twelve to twenty-six hours 



