242 Animal Intelligence 
depends upon some particular difference in the animal. Each 
immunity, for example, has its detailed representation in an 
altered condition of the blood or other bodily tissue. In 
general the changes in an animal which cause changes in its 
behavior to the same situation are fully enumerated in a 
list of the bodily changes concerned. That is, whatever 
changes may be supposed to have taken place in the animal’s 
vital force, spiritual essence, or other magical bases for life 
and thought, are useless for scientific explanation and con- 
trol of behavior. 
No competent thinker probably doubts this in the case of 
such changes as are referred to by hunger, sleep, fatigue, so- 
called ‘functional’ diseases and immunity, and those who do 
doubt it in the case of mental growth and learning seem to 
represent an incomplete evolution from supernatural, or 
rather infrascientific, thinking. There may be in behavior 
a surplus beyond what would be predictable if the entire 
history of every atom in the body was known — a surplus 
necessarily attributable to changes in the animal’s incor- 
poreal structure. But scientific thinkers properly refuse 
to deliberately count upon such a surplus. 
Every response or change in response of an animal is then 
the result of the interaction of its original knowable nature and 
the environment, ‘ .This may seem too self-evident a corollary 
for mention. It should be so, but, unfortunately, it is not.) 
Two popular psychological doctrines exist in defiance of it. 
One is the doctrine that the movements of early infancy are 
random, the original nature of the animal being entirely 
indifferent as to what movement shall be made upon a given 
stimulus. But no animal can have an original nature that 
does not absolutely prescribe just what the response shall 
be to every stimulus. If the movements are really random, 
they occur by virtue of some force that works at random. 
