August, '12] BRLES AND SHF.PPAKD: IXFAXTILE PARALY.-^Id 311 



kissing-bugs, etc.) that their presence could hardly l)e overlooked. 

 The spoiadic occurrence of the disease and its failure to spread mainly 

 in infected houses, serves to eliminate the wingless species, and the 

 failure generally to find a history of painful insect bites, shows that 

 Reduviid bugs cannot be to blame. 



The Coleoptera do not ordinarily frequent substances which contain 

 bacteria and it is only in rare instances that they can cause Infection 

 by biting, and it is very unlikely that any species will ever prove to be 

 specific carriers of any human disease. 



The Diptera include the largest number, and far and away the most 

 widespread and important disease carriers among insects. These 

 group themselves from an entomological standpoint into several 

 series. 



Mosquitoes. These insects serve as specific carriers of such dis- 

 eases as yellow fever, malaria and filariasis, and might readily be 

 suspected in the present connection, since numerous species are 

 common in all regions where acute epidemic poliomyelitis occurs. 

 Malarial fevers and yellow fever occur normally in epidemic form, each 

 associated with the presence of the particular species of mosquito 

 which is necessary to the completion of the life cycle of the pathogenic 

 organism. The mosquito obtains it from the blood of one patient, 

 and later injects it into another person, after the life cycle has been 

 completed within the body of the mosquito. The malarial organism 

 is a well-known protozoan and its development within the body of its 

 insect host is quite familiar, but the organism of yellow fever, is a 

 filterable virus concerning which we know nothing definitely, except 

 that a twelve-day incubation period is required in the mosquito before 

 its bite becomes infectious to a second person. It will be noticed that 

 this organism resembles the virus of anterior poliomyelitis in being 

 filterable. 



There are several facts associated with mosquito-borne diseases 

 which are at great variance with some observed in studies of poliomye- 

 litis. In the first place, yellow fever and malaria spread rapidh' in 

 infected districts and quickly involve a large percentage of the popu- 

 lation unless rationally controlled, and this is to be expected from the 

 universal abundance of the insect hosts and the great opportunities 

 of infection enjoyed by them in the presence of a human case of the 

 disease. Such is not true of poliomyelitis, for although this becomes 

 truly epidemic, it is never disseminated so thoroughly and rapidlj' 

 throughout a community. In the second place, adults are fully as 

 apt to be bitten by mosquitoes as are children, yet poliomyelitis has 

 been considered essentially a disease of childhood and young adult 

 life. (This assumes equal susceptibil'ty to infection at all ages, which 



