180 GENERAL BIOLOGY 



to some definite plan which will show that it has profited by past ex- 

 perience. 



In this connection one is also confronted with difficulties as in 

 other fields. Suppose one is attempting to see wheth'er an animal can 

 distinguish between colors and then learn to go to one hue rather than 

 to another. Suppose now, that the animal does not show any more 

 inclination of going toward one color than toward another. This by no 

 means proves that the animal cannot distinguish, or is unable to learn, 

 that there are two colors. It may mean nothing more than that colors 

 make so little difference to the animal that there is no reason (motive) 

 for his choosing one rather than the other. In such an instance the ani- 

 mal's reaction to both colors would be identical, and one could prove 

 little or nothing from its behavior. 



Another animal may be thought unable to learn because it tries a 

 problem a few times and then ceases to react at all to the stimulus. This 

 may be due entirely to fatigue on the part of the organs used, and not 

 to inability to learn. That is, the nerve receptors may become dulled 

 or tired by new stimuli which are foreign to the animal in its native 

 career. 



Or again, some sensation may be pleasant to an animal only if sec- 

 ondary factors are present, such as the taking of food only when fmngry 

 or when the body is in good health. But surely the rejection of food 

 does not mean that the animal either can or cannot discriminate between 

 foods. We often will not eat one kind of food, while another is relished, 

 or we often will just as readily eat ice-cream, candy, or fruit, and show 

 just as much desire for the one as for the other, but this certainly does 

 not mean that we do not know the difference between these three types 

 of edibles. 



Then, too, the state of health makes a tremendous difference in 

 what an animal will choose. Dogs and cats eat certain plants at certain 

 times but at other times they will not touch them. But do they not 

 know the difference between these plants and other food? 



Then, too, an animal may be trained to do certain things, but sup- 

 pose it does these things without having been trained. Can one not 

 argue as well that the animal merely stumbled upon doing the act, and 

 then doing it often, the nerve-arcs became fixed and the animal can no 

 longer help itself? It is now a habit. 



Habits are but acts performed by fixed nerve-arcs. 



The question may arise as to what difference there would be be- 

 tween psychology and physiology if all we are to study consists of 

 nerves and reactions. Really, there would be no difference in content 

 of the two sciences, the difference would consist in emphasis. The 

 psychologist lays stress on emotions, feelings, etc., and the physiologist 

 on the simple observable reaction which follow a given stimulus. The 

 psychologist, in other words, wants to know how the animal feels and 



