20 



INTRODUCTION. 



applied to a disease in which the larvae of various species of 

 insects are found in the human body, but these appear to be 

 entirely accidental cases, wherein these larvae have been 

 injected. A species of (Estrus, in like manner, has been 

 found to be parasitic within the bodies of persons residing in 

 the tropics, but this (although it has received the name of 

 (Estrus hominis) I should be rather induced to regard also 

 as an accidental locality selected by the insect, instead of its 

 real habitat. There is another tribe of insect enemies whose 

 attacks are not less annoying, although not resulting, like 

 the former, from a desire to feed upon our bodies. Here 

 are to be ranked the bees, wasps, and other insects provided 

 vdth poisonous stings, which, however, they seldom employ 

 except in their own defence, or to resent injuries offered 

 to them. Here also may be added the spiders, whose 

 powerful jaws are equally provided with a poisonous fluid, 

 as well as the scorpion, whose long and jointed tail is de- 

 fended at the tip vvdth a powerful sting. Other insects are to 

 be ranked amongst our minor miseries, namely, those which 

 by the emission of a caustic or disgusting fluid, operate 

 strongly upon our olfactory nerves. But the tribes of insects 

 which prey upon our cattle are equally numerous, including 



Gasteropliilus equi. 



1 - a 



Gasterophilus haeraorrhoidalis. 



fleas of different species, ticks, gadflies, forest flies, and 

 especially the remarkable family of (Estrideous flies, the 



