152 MODIFICATIONS OF BEHAVIOR 
but carry the process down the scale of life and it begins to 
take on the character of other organic regulations such as we 
find in the tissue cells of our own bodies; for even there the 
intake and assimilation of nutriment is regulated as in free 
organisms. In none of the animals we have described is 
there evidence of intelligence in the selection of food. The 
choice made is more readily explained in terms of what 
Bohn calls differential sensibility. The organism is so con- 
structed that it responds to certain kinds of stimuli in one 
way and to other kinds of stimuli ina different way. But it 
also has the faculty of responding to the same stimulus in 
different ways at different times. Here it may be assumed 
that the different response is the effect of changes of internal 
conditions which alter the irritability of the animals. The 
stimuli set up by the presence of food in the digestive tract, 
the secretory activity of the cells, the processes of absorption 
and assimilation going on throughout the body afford a 
complex of influences affecting the neuro-muscular mechan- 
ism and naturally modifying its action. 
In the sea anemones, contact tends to set in operation 
one or the other of two mechanisms—one involved in taking 
in food, the other in its rejection. These mechanisms are 
mutually inhibitory and often there is a struggle between 
them resulting in a hesitation or vacillation in the response 
of the organism. Internal conditions act as a sort of brake 
on one or the other mechanism and thus change the nature 
of the response to a particular external stimulus. 
This type of behavior which has often been assumed to 
indicate consciousness if not intelligence is not anything 
which cannot be accounted for on the basis of reflex action. 
It is a type of behavior which is wide spread, in fact probably 
coextensive with animal life. If it is a criterion of intelli- 
gence we must assume that all animals are intelligent and 
