17 
In practice, indeed, it is to this system of living nature as 
, affecting insects, and through them as affecting man, that he must 
give his principal attention; for the more the scientific cecologist 
studies the natural order of life the higher is his respect for the 
scheme of adaptations and adjustments which it everywhere ex¬ 
hibits, the more apprehensive he becomes of the consequences of 
ignorant interference with the settled workings of this system, 
and the more clearly he sees that, since much interference is in¬ 
evitable, its consequences must be clearly understood, and means 
must be devised to correct such reactions as are likely to have a 
harmful issue. 
The study of oecology is thus to the economic entomologist what 
the study of physiology is to the physician. Human interference 
with the natural order of plant and animal life gives rise to reac¬ 
tions which correspond closely to those of bodily disease. What 
physiology is to medicine, that oecology is to economic entomology. 
As the old medicine was chiefly a matter of drugs and empirical 
dosage, so economic entomology was not long ago almost wholly 
a matter of insecticides and mechanical methods of destruction. 
The new economic entomology, on the other hand, like modern 
medicine, seeks diligently, first, to avoid all unnecessary disturb¬ 
ance of the normal play of life, and, second, to direct the powers 
of nature herself, so far as possible, to the correction of such dis¬ 
orders as are nevertheless likely to arise. 
PARASITISM OF INSECTS. 
Many of the natural checks upon the inordinate multiplication 
of insects, and thus upon the disturbing consequences of such ex¬ 
cess, are beyond our present control or influence,—those interposed 
by the weather, for example,—but one of the most powerful of 
them all, may apparently be brought more or less completely un¬ 
der our control. When all other restraining agencies fail or prove 
too weak to check an insect outbreak, parasitism by other insects 
or by plants is one of nature’s last and sovereign expedients; and 
this remedy never fails finally to reduce the too prolific species to 
its proper place. 
To gain control of this great natural agency, to apply it to the 
correction of the disorders which we have ourselves induced, 
and even to improve by its means and for our purposes the 
natuial oecological system of the world, is one of the present 
P u° ble S S ° f the econ ? mic naturalist. It is along this line that 
the greatest advances in modern medicine have been made,—the 
. , , t _ ever seen in this oldest of the biological 
sciences, and it is along this line that the economic entomologists 
of this country and of Europe are now beginning to work, in the 
hope of doing for the labor of men something like what has been 
done by the physician for their lives. UfifitoA.-i 
The most destructive parasites of insects may be divided bio¬ 
logically into three principal classes—insects, Protozoa, and fungi. 
—2 S. E. 
