244 INSECTS AND DISEASE 



The value of such precautionary measures has been 

 abundantly demonstrated in several instances, and justi- 

 fies the belief that henceforth it will be possible not only 

 greatly to reduce the number of cases, but to prevent the 

 spread of the disease. 



Other Insects and Disease. — Once more attention 

 is directed to the fact that most insects are harmless, 

 and the comparative few that are known to transmit 

 disease can be kept within bounds when a community 

 exercises a reasonable amount of care. But unfortu- 

 nately there are communities where cleanliness is not 

 a virtue, and lice, bedbugs and cockroaches flourish. An 

 examination of these insects amid such surroundings 

 discloses the fact that they, like the fleas, often carry on 

 their bodies large numbers of disease-producing germs, 

 and it is now thoroughly established that typhus and 

 the related trench fever are carried by lice. There is 

 also considerable evidence that plague and infantile 

 paralysis are borne from one animal to another by the 

 bedbug. Tuberculosis, typhoid fever and Asiatic cholera 

 are believed by some scientists to be spread by cock- 

 roaches. And there are several other diseases, attack- 

 ing man as well as many domesticated and wild animals, 

 where insects are strongly suspected of being the means 

 of distribution. 



Mites, Ticks and Disease. — Although these organ- 

 isms are more closely related to the spiders than they are 

 to the insects, their habits and methods of transmitting 

 disease are so similar that they may be conveniently 

 treated in this chapter. The mites are not certainly 

 known to transmit disease in man, but the fact that 

 they are responsible for itch, scab, mange and other skin 

 disorders brings them under suspicion. The ticks are 

 invariably voracious parasites which pierce the skin of 

 the victim with needle-like mouth parts and gorge them- 

 selves with blood. In this operation they may suck up 

 minute organisms which produce a considerable number 



