4 On Some Interactions of Organisms. 
terdependence of its parts, on the other hand, it differs 
from the single animal in the fact that, notwithstanding 
this intimate and instant sympathy of part with part, it 
has an immense vitality. To cut off the leg of an animal 
is often sufficient to destroy its life, hut one might cut 
off the head of the animal world, so to speak, without 
seriously impairing its energy. Suddenly to annihilate 
every living vertebrate would doubtless set on foot some 
tremendous revolutions in the life of the earth, but it is 
certain that in time the wound would heal — that Nature 
would finish by readjusting her machinery and would 
then go on much as before. In fact, any subkingdom of 
animals or any class of plants might thus be struck out, 
without the slightest danger that terrestrial life would 
perish as a consequence. The functions of the missing 
member would be taken on in part by other members, 
and in part be rendered needless by new adjustments. 
We see many present illustrations of this fact, as in 
Australia, where there is but one native carnivorous ani- 
mal, and that probably not indigenous ; in several Pacific 
islands where mammals are unknown; and in New Zea- 
land and the Galapagos, where insects are extremely few 
and the flowers, therefore, chiefly colorless and odorless. 
We see, likewise, illustrations of the same truth in the 
conditions of vegetable and animal life in earlier geologi- 
cal periods. Plants and insects, for example, existed to- 
gether through vast periods of time when there were 
neither mammals nor birds on earth to supervise or 
regulate their relations. 
If this is true of such immense and revolutionary dis- 
turbances, it is all the more certain that this same spon- 
taneous action of natural forces must in time reduce the 
smaller disturbances of the primitive order caused every- 
where by civilized man, and must end by adjusting the 
whole scheme of organic relations to his interests as com- 
pletely as to the interests of any other species. It is also 
plain that if man understands clearly the disorders which 
arise in the system of Nature as a result of the rapid pro- 
gressive changes in his own condition and activities, and 
understands also the processes of Nature which tend to 
