ACTIVITY AND ENVIRONMENT 27 
the same living substances into different special organs would of necessity 
give different organisms different properties. 
Different chemical substances often behave differently under a given 
condition of temperature, pressure, or light, etc. Likewise, if a cockroach 
and a house fly are liberated in the center of a room, the fly goes to a 
window and the cockroach into a shadow; furthermore, a cold night will 
kill the house fly, while to dispose of the cockroach the proverbial two 
wooden blocks are necessary. Both differences in physiological char- 
acter (behavior) are due to differences in the organisms. Different 
organisms often behave differently in the same intensity of the same 
physical factor, for example, the same temperature or light, just as the 
different chemical substances do. Different chemical substances often 
undergo different changes with variations in temperature, pressure, or 
light. Each has its characteristic reactions. Still whole groups may be- 
have quite similarly. Changes in conditions affect organisms. We have 
all noted the effect of a cool day upon the activity of animals such as the 
insects. Different organisms usually behave differently in some respects, 
while whole communities may behave quite similarly in other respects. 
a) The organism as unaffected by the environment.—When all of the 
external conditions continue approximately the same, the activities of 
the organism are called spontaneous (35, p. 347). As has been stated, 
the organism is naturally active. Accordingly, movements may possibly 
take place as a manifestation of the released energy inside the animal, 
or of disturbances and changes in the organism which are not directly 
initiated by the environment. Probably animals often move without 
any external stimulation (44, chap. xvi). One who has observed the 
wonderful Japanese dancing mice knows that their constant movement 
may not be the result of the external conditions, but of the energy which 
is expended within the organism. 
Jennings (44) stated that these spontaneous movements must be 
recognized in the study of behavior, and that many errors have arisen 
from their neglect. If we see an animal moving, we should not assume 
that it is moving because of some external condition acting on it at the 
time. It may be due to previous stimulation or it may be the result 
of internal conditions. Growth, maturity, reproduction, and death are 
accompanied by changes in behavior, structure, etc. All may take place 
without great change in environment. 
b) The organism as affected by the environment.—Many organisms are 
not sensitive to slight changes in the external environment. Having 
