48o GENERAL BIOLOGY 



vided for and predetermined in their organization. The 

 acts most fundamental to the preservation of races, feeding, 

 reproduction, etc., are thus provided for in the main in all 

 animals. A kitten is instantly thrown into a paroxysm of 

 defensive movements and attitudes at the first sight or smell 

 of a dog. A chicken flees at the first cry of a hawk, although 

 it may be quite unresponsive to the (to us apparently) simi- 

 lar cry of a catbird. Nature has developed this nice dis- 

 crimination by the elimination of the unresponsive. Racial 

 experience has thus been incorporated into the organism in 

 such manner that vitally important stimuli dominate all the 

 activities of the body and enable it automatically to meet 

 the chief exigencies of life. There is, however, especially in 

 the higher animals, a field of activity in which reactions are 

 less stereotyped; more variable; and here lies the oppor- 

 tunity for learning by individual experience. This is so 

 large a part of our own life that we have difficulty realizing 

 how limited it is in many of the lower animals. 



The sight of food that is not within reach may stimulate to 

 activities that are predetermined only for the act of feeding, 

 and the processes of nutrition ; not at all for the method of 

 getting at the food. A horse confined in a bare lot, is 

 stimulated to a great variety of activities by the sight of the 

 green grass on the other side of the fence. He does many 

 things that yield no satisfactory results; he pushes, he 

 whinnies, he stamps, he tugs at the toprail with his teeth, he 

 rears, etc. But by chance he lifts the latch of the gate with 

 his teeth, and this act is accompanied by pleasurable results; 

 he sees the gate open. A^nother time he is likely to concen- 

 trate his efforts at the gate, and to lift the latch sooner, with 

 fev/er ineffective efforts. Every repetition of an act makes 

 its subsequent performance easier, especially when accom- 

 panied by pleasurable experiences accompanying successful 

 performances of it. Soon he is able to eliminate all the un- 



