On Some Interactions of Organisms. 13 
foe. Especially does the wonderful locomotive power of 
birds, enabling them to escape scarcity in one region, 
which might otherwise decimate them, by simply passing 
to another more favorable one, without the loss of a life, 
fit them, above all other animals and agencies, to arrest 
disorder at the start — to head off aspiring and destruc- 
tive rebellion before it has had time fairly to make head. 
But we should not therefrom derive the general, but 
false and mischievous, notion that the indefinite multi - 
plication of either birds or predaceous insects is good. 
Too many of either is nearly or quite as harmful as too 
few. 
And this brings us to the application of these principles 
to the interests of civilized man. We must note how the 
new forces which he brings into the field expend them- 
selves among those we have been studying, and to what 
reactions they are in turn subjected. We must first see 
how far the primitive natural order of life lends itself to 
the supply of man’s needs, to the accomplishment of his 
purposes; and must determine, in a general way, where 
he may be content to leave it undisturbed, where he should 
address himself to its improvement, and where he is com- 
pelled to attempt wholly to set it aside, substituting arti- 
ficial arrangements of his own, devised solely in his own 
interest. 
Some of Nature’s arrangements man finds himself un- 
able to improve upon for his own benefit. No one thinks 
of cultivating the forest to hasten the growth of the 
wood, or of trimming the wild oak or the maple, or of 
planting artificially the nuts and acorns in the woods to 
increase the number of the trees. 
We are content to leave things there to go on essential- 
ly in the old way, merely anticipating the processes of 
natural death and decay by removing the trees before they 
spontaneously perish, and glad if the revolutions of or- 
ganic life which we set up in the country around do not 
penetrate to the forest, visiting the leaves and trunks of 
the trees with the scourge of excessive insect depredations. 
Usually, however, we find the ready-made system of 
Nature less to our liking, and all our cultures are at- 
