Tin: DISPLAY OF i:nkr(;y :m 



stimulus but by the aggregate of all the stimuli which impinge upon 

 it. The stimulus pattern causes the behavior pattern. The fact 

 that organisms behave in a purposeful way and that frequently their 

 behaviors are modified or "conditioned," has given rise to the point 

 of view that behaviors are adaptive. 



To understand this philosophy it is necessary to go back to the Avork 

 of Child. In recent years he has shown that all organisms exhibit a 

 definite polarity. Even in a single-celled organism, polarity is shown 

 not only in an anterior and posterior end, but also in a physiological 

 gradient which extends from the surface to tlie interior. The proto- 

 plasm at the surface exhibits the highest rate of metabolism, the 

 protoplasm near the center the lowest rate. If the organism is cut 

 in two, a new center forms as far away from the surface as possible 

 and a new field of metabolism comes into existence. 



The following test of this metabolic gradient was made with flat- 

 worms, animals so simple in structure that they lend themselves 

 readily to experimentation. After removing the head and tail end of 

 a number of worms, the remaining part of the worm was cut into four 

 pieces, as many as a hundred worms at a time being used in the 

 experiment. After sorting the cut pieces into groups of anterior 

 sections, second, third, and fourth sections, it was found that the 

 metabolic rate in these groups was constant, the most anterior group 

 using the most oxygen and giving off the most carbon dioxide. The 

 most posterior group used the least oxygen and gave off the least 

 carbon dioxide. There was thus a chemical gradient of physiological 

 activity correlated with the nervous differentiation of the organism, 

 the latter acting as a physiological unit and not as a cell aggregate. 



Physiological gradients are seen every^vhere. Eggs exhibit polarity, 

 the potential energy at one end being much greater than at the other. 

 Gland cells are j^olarized so that they always secrete in a certain 

 direction, while nerve cells in higher animals invariably conduct 

 impulses in only one direction. In embryos, an early polarization 

 takes place and, as we have seen, all animals except radially sym- 

 metrical ones exhibit polarity. 



The beginnings of behavior in embryonic animals start as mass 

 movements of the organism as a whole. This has been found to be 

 due to the fact that the central nervous system has not grown out 

 into the surface of the body. A new group of behaviorists start with 

 the general thesis that behaviors, such as tropisms, are organized 

 responses to a total pattern of stimuli, the organism modifying its 



