ANIMALS AND THEIR ENVIRONMENTS ADAMS. 



523 



have reached a certain stage is said to be satiated; later it is in the 

 condition of incipient hunger; and still later, in the physiological 

 condition of intense hunger. These internal changes cause the ani- 

 mal to react very differently to any food which is in its immediate 

 vicinity. These changes in physiological conditions are strictly 

 comparable to the change which an animal passes through in its 

 ontogeny; to the life cycle of an insect, for example, in which the 

 physiological conditions and behavior of a caterpillar are very differ- 

 ent from those of the pupa and of the adult or moth. One of the 

 higher animals, a dog, for instance, will undergo internal changes 

 which will completely alter its responses at the sight of an old rival 

 or enemy. Such considerations as those just cited show clearly that 

 extensive internal physiological changes take place in animals, and 

 that while some of them are very gradual others are exceedingly 

 rapid. These internal conditions or changes have been well char- 

 acterized by Jennings (1906:289) as follows: 



The " physiological state " is evidently to be looked upon as a dynamic con- 

 dition, not as a static one. It is a certain way in which bodily processes are 

 taking place, and tends directly to the production of some change. In this 

 respect the " law of dynamogenesis," propounded for ideas of movement in man, 

 applies to it directly (Baldwin, 1897:167) ; ideas must indeed be considered so 

 far as their objective accompaniments are concerned, as certain physiological 

 states in higher organisms. The changes toward which the physiological state 

 tends are of two kinds. First, the physiological state (like the idea) tends to 

 produce movement. This movement often results in such a change of condi- 

 tions as destroys the physiological state under consideration. But in case it 

 does not, then the second tendency of the physiological state shows itself. It 

 tends to resolve itself into another and different state. 



I may thus summarize the relation of metabolic processes to 

 physiological conditions and processes of behavior by the following 

 table. 



Table 1. — The dynamic relations of animal activities. 



Changes in the internal conditions are produced also by external stimuli. 



