CHAPTER IX 
INsEcTS aS CARRIERS OF DISEASE 
WITHIN comparatively recent years careful study has been given 
to insects as carriers of human disease, with the result that astounding 
facts have been disclosed. We know to-day that several of the serious 
and fatal diseases that afflict man, and several others to which domestic 
animals are subject, are carried or transmitted by insects; and in some 
cases the disease is carried in no other way. The study of these facts 
and possibilities constitutes the new Medical Entomology. 
House Flies 
Beyond doubt the commonest and the worst offender is the house 
fly. Both observed facts and careful experiments have proved that 
this insect is instrumental in 
the spread of typhoid fever, 
tuberculosis, and certain intes- 
tinal diseases, and there is every 
probability that further study 
will reveal others. 
The habits of the fly in its 
choice of breeding places, its 
irrespressible tendency to enter 
our houses and walk over our 
food, and the structure of its 
body, especially its feet and its 
tongue, form thechainof circum- 
stances by which the transfer of disease germs is brought about. The 
same fly that spent its larval life as a maggot in filth or infected excre- 
42 
Fic. 42.— The House Fly, Musca domes- 
tica Linn. Enlarged. Original. 
