Jantjaet 7, 1910] 



SCIENCE 



13 



With the anticipatory phase, however, 

 the case is quite different. The more com- 

 plex the feeding act becomes, the more 

 prolonged and difSeult is this phase of the 

 process. In the case of carnivorous verte- 

 brates the prey must be recognized at a 

 distance and carefully stalked and at- 

 tacked from the most advantageous side, 

 and all of these details will vary with 

 each trial. No combination of simple re- 

 flex arcs can be laid down in advance 

 within the nervous system which will be 

 adequate to meet the infinite variations of 

 these problems. 



We may hypothecate the course of the 

 evolution of this reaction as follows: In 

 the lower animals, as in the spinal cords of 

 the higher ones, the whole formatio reticu- 

 laris, or correlation tissue, is relatively un- 

 specialized and receives all kinds of aifer- 

 ent impulses from the primary sensory 

 centers ; these in turn it delivers over to the 

 final common efferent pathways. There is 

 thus a constant collateral avenue of nerv- 

 ous discharge through the reticular for- 

 mation parallel with that in the primary 

 reflex arcs and reinforcing, inhibiting or 

 otherwise modifying these primary simple 

 reflexes. 



The character of the efferent discharge 

 from this reticular formation will depend 

 upon the sources and strength of the affer- 

 ent impulses, the fluctuating internal re- 

 sistance of the chains of neurones of which 

 it is composed and other variable factors, 

 some of which, like the resistance at the 

 neurone thresholds, may be modified, as 

 already pointed out, by repetition of func- 

 tion (habit formation). 



The suprasegmental correlation centers 

 present essentially the same dynamic as- 

 pect, but with the afferent pathways more 

 sharply defined and limited and the whole 

 more perfectly adapted to effect definite 

 types of more complex correlation. Thus, 



the thalamus becomes a great center for 

 the correlation of somatic reflexes and the 

 hypothalamus for visceral and olfactory 

 reflexes. Accordingly, all of the lower 

 primary correlation centers send strong 

 secondary tracts upward into the dien- 

 cephalon. 



Now to return to the feeding activities, 

 so far as these are contact reactions, such 

 as nosing about in the mud for food, the 

 interval between the anticipatory and con- 

 summatory phases is not necessarily long 

 and a very simple reflex mechanism is 

 adequate to distinguish between food and 

 other objects. 



But in the more complex cases the inter- 

 val between the anticipatory and consum- 

 matory phases is occupied by the discharge 

 into the higher correlation centers of a 

 series of momentarily changing stimuli 

 from the distance receptors, and the later 

 acts of this phase will be the resultants of 

 all of these influences plus the effects in the 

 centers themselves of vestiges of similar 

 reactions in the past. The whole system 

 is in a state of neural tension which varies 

 constantly as new impulses from the per- 

 iphery reverberate through its substance. 

 The high neural resistance of this complex 

 tissue raises the threshold of discharge 

 from it so that a certain summation of 

 stimuli takes place before the tension is re- 

 lieved by a discharge of the neural energy 

 into the lower mechanism of the consum- 

 matory reaction, which is already so ad- 

 justed as to perform its functions when 

 once actuated more or less mechanically 

 and therefore without the development of 

 such internal resistance as characterizes the 

 anticipatory mechanism. 



In the storm and stress of this interval 

 just preceding the consummatory reaction 

 the higher mental faculties are born. 



The stream of nervous influences pour- 

 ing into the higher correlation centers from 



