APPETITES AND AVERSIONS. 95 



will follow, for each appetite is distinguished by its own expres- 

 sive signs (consisting partly of the incipient consummatory 

 action), and one can see which appetite is gaining control of the 

 organism. 



These outward expressions of appetite are signs of physio- 

 logical states which are but little known. Since my own obser- 

 vations have been on external behavior only, I say little about 

 the internal states. They are probably exceedingly complex 

 and numerous and similar to the physiological states which in the 

 human organism are concomitants of appetites, 1 emotions, de- 

 sires. They doubtless include stimulations from interoceptors 

 and proprioceptors ; perhaps automatic action of nerve centers; 

 perhaps readiness or unreadiness of neurones to conduct. It is 

 known that some of the periodic appetites are coincident with 

 profound physiological changes. Thus Gerhartz ('14) found that 

 during the incubation period in the domestic fowl the metab- 

 olism of the body as a whole is at a low ebb. In some cases a 

 stimulus from the environment is the immediate excitant of an 

 appetite; especially, stimulation of a distance-receptor may arouse 

 appetite for a contact stimulus, as when the sight of food arouses 

 appetite for the taste of it. But probably in every case appetite 

 is dependent upon physiological factors. And in many cases 

 the rise of appetite is due to internal causes which are highly 

 independent of environmental conditions, and even extremely 

 -resistant to environmental interference. 



Appetitive behavior in vertebrates is evidently a higher 

 development of what- Jennings ('06, p. 309) calls the positive 

 reaction in lower organisms; aversive behavior in vertebrates 

 corresponds to what Jennings (p. 301) calls negative reactions. 



The attempt to distinguish between instinct and appetite, 

 as in Baldwin's Dictionary ('01), is not justified by the facts of 

 behavior. Baldwin says : "Appetite is distinguished from in- 

 stinct in that it shows itself at first in connection with the life of 

 the organism itself, and does not wait for an external stimulus, 

 but appears and craves satisfaction." These characteristics, 



1 Hunger furnishes a typical case of appetitive behavior (Carlson, '16; Ellis 

 '10, 198-199). Carlson makes a distinction between hunger and appetite. The 

 distinction he finds is certainly real, but the use of words is unfortunate, for hunger 

 is clearly one kind of appetite. 



