102 INSTINCTIVE BEHAVIOUR 
this position, and agree to use the term “instinct” for our 
present purpose in a comprehensive sense, we may now proceed 
to consider very briefly the nature of the elements which enter 
into the instinctive situation. 
First, there are the external stimuli affecting one or more 
of the sense organs, and thus evoking consciousness ; and 
secondly, there are internal factors, having their source in the 
condition of the body, or its parts and organs. It is con- 
venient to take these two together, so that we may see what 
relationship they bear to each other. Both seem to be present, 
and to co-operate in a great number of instinctive acts. In 
the behaviour connected with feeding, for example, an internal 
element of hunger co-operates with the external presentation 
of the appropriate food or prey. So, too, with the instincts 
concerned in the propagation of the race. Looking at the 
matter generally, we may regard the internal factors of the 
kind with which we are now dealing, as giving rise to a want 
or need, passing in some cases into a state of craving. In 
themselves such conscious states are in their inception ex- 
ceedingly indefinite ; for a want can only be rendered definite ~ 
in experience by its appropriate satisfaction. In many cases 
of instinctive behaviour the indefinite want and the particular 
and duly related stimulus seem to lead, without prevision and 
by a blind impulse, to the performance of those acts which 
will afford the unforeseen satisfaction. And when once this 
satisfaction has been attained, subsequent wants or needs of 
like character will no longer be indefinite ; nor will future 
behaviour of the same kind be thereafter wholly instinctive, 
for it can never again be prior to, or independent of, experience. 
Granted, however, that a felt need of some kind, indefinite 
at first but none the less real, is present in many cases as a 
spur to instinctive behaviour ; is it in all cases a necessary 
factor ? May we say that this distinguishes instinctive from 
merely reflex action ? The question is, from the nature of the 
case, exceedingly difficult to answer. But without going so 
far as to say that reflex action may be unerringly distinguished 
from instinctive behaviour by the absence of any such internal 
