8 FREDERICK S. BREED 



a black cardboard for their pecking tests. Our knowledge of 

 the time of appearance of the various instincts should not be 

 left to depend entirely upon chance stimuli. Who shall say 

 that a given reaction might not have occurred much earlier 

 if the appropriate stimulus had been provided? 



The chicks, while still in the incubator, are known to be posi- 

 tively photo tropic. The inctibator trays that have near the 

 glass door a trap through which the chicks fall to a screen below, 

 depend for their effectiveness on the fact that the chicks crowd 

 toward the light. 



B. Drinking 



a. Problem. — In the study of ,instincts from the objective 

 point of view, interest naturally centers first in function, second 

 in structure. The activities which are known as instinctive 

 must be analyzed into component units of behavior, of which 

 they are nearly always complexes. Furthermore, no account of 

 instinct will be satisfactory, no explanation complete, until we 

 understand the structure of the machinery involved in each 

 action. But so much accomplished, this is not all. These 

 structures are not of such a nature that they in some way get 

 themselves into action. So far as we know, they have no in- 

 herent principle of spontaneity. Intra- or extra-organic stimuli 

 are necessary to touch them off. Environment in the form of 

 energies external to the structures and additional to the func- 

 tions seems to be a sine qua nOn. Hence a complete under- 

 standing of instinctive actions will include a detailed knowledge 

 of the " objects " in conjunction with which the particular 

 activities manifest themselves. In the following bit of work 

 on the instinct of drinking, consideration of the problems of 

 function and structure is made secondary to an inquiry into 

 the nature of the extra-organic stimulus. 



b. Method and Tests. — Chicks no. 69 to no. 81, inclusive, 

 were hatched during the afternoon and evening of Dec. 2 and the 

 morning of Dec. 3, 1908. Beginning with Dec. 3, their pecking 

 had been tested in the regular manner each day. As the animals 

 finished the first pecking tests they were marked, numbered, 

 and transferred from the incubator to the brooder. Although 

 given food and freedom to run about in the litter, they were 

 allowed nothing at all to drink until tested as described below, 

 neither were they permitted to see other chicks drink. A pos- 



