IMPULSE, INTEREST, AND EMOTION 239 
of such acts do so likewise. And coalescent association not 
only links and groups the elements within the situation called 
forth by the single act, but comprises also the elements of the 
developing situation afforded by the whole series. We see this 
in the young chick, where, as the result of experience, attention 
is emphasized where the material is palatable, and lapses where 
it is nauseous—such nauseous substances being soon ignored. 
Furthermore many environing things appeal in different ways 
to the same limited number of sense organs, while the same 
motor organs respond in different ways in successive modes 
of instinctive behaviour. The same brain forms the physical 
basis of varied situations overlapping in many ways, and 
receives afferent messages from the same body. Hence, in 
its organic unity it affords the conditions for an underlying 
stratum of mental unity, amid all the diversities of experience ; 
while the multiplicity of messages on the one hand from 
external things, and on the other hand from internal happen- 
ings, lays the foundations of a differentiation between the 
external world and the self—a differentiation long to remain 
implicit, and only to be rendered explicit on a far higher level 
of mental development. For at this early stage, and perhaps 
throughout animal life, “there is no single continuous self con- 
trasted with a single continuous world. Self, as a whole, 
uniting present, past, and future phases, and the world as a 
single coherent system of things and processes, are ideal con- 
structions, built up gradually in the course of human develop- 
ment. The ideal construction of self and the world is com- 
paratively rudimentary in the lower races of mankind, and it 
never can be complete. On the purely perceptual plane [with 
which we are now dealing] it has not even begun.”* But 
though the ideal constructions of self and the world have not, 
as Dr. Stout says, at this stage, even begun, yet, as the same 
author observes,t “animals distinguish in the environment, and 
‘treat as a separate thing, whatever portion of matter appeals to 
their peculiar instincts, and affords occasion for their charac- 
teristic modes of activity.” And this differentiation of specially 
* G, F. Stout, “ Manual of Psychology,” p. 268. t Ibid., p. 318. 
