Fig. 36—Body-louse (Pediculus vestimenti). (From drawing by J.H. Paine.)
HOW INSECTS MAY CARRY DISEASE GERMS
Insects may carry the germs or parasites which cause disease in a purely mechanical or accidental way, that is, the insect may in the course of its wanderings or its feeding get some of the germs on or in its body and may by chance carry these to the food, or water, or directly to some person who may become infected. Thus the house-fly may carry the typhoid germs on its feet or in its body and distribute them in places where they may enter the human body.
Several other flies as well as fleas, bedbugs, ticks, etc., may also carry disease germs in this mechanical way. While this method of transmission is just as dangerous as any other, and possibly more dangerous because more common, another method in which the insect is much more intimately concerned is more interesting from a biological standpoint at least and will be discussed more fully in the chapters on malaria, yellow fever and elephantiasis.
In these cases the insect is one of the necessary hosts of the parasite, which cannot go on with its development or pass from one patient to another unless it first enters the insect at a certain stage of its life-history.
Fig. 37—One use for the house-fly.
BABY-BYE.