LIGHT DISCRIMINATION IN THE ENGLISH SPARROW 85 



means of a system of cords and pulleys leading to the front 

 end of the apparatus. 



Two centimeters above the floor of the large discrimination 

 chamber and four centimeters apart are perches across the box. 

 The perches were made of three-eighth inch 22 gage brass tubing, 

 oxidized and slit longitudinally into two halves. The two halves 

 of this tubing were placed on either side of a .5 inch wooden 

 core and held in place with paraffine. One-half of each perch 

 is connected to one terminal and the other half to the other 

 terminal of a Williams' Dial induction coil whose primary is 

 in circuit with two dry batteries. A hand key is placed in the 

 circuit and the secondary coil shifted to a position so that when 

 a bird is resting on a perch it may be shocked by closing the 

 circuit at the key. It is natural for the bird to hop from one 

 perch to another and grip the perch with the feet. So when the 

 feet are moist they can be shocked very effectively. A wet pad 

 is kept in the entrance chamber C (Fig. 1) to keep the bird's 

 feet moist. When dry the horny epidermis serves to protect 

 them from the electric discharge. 



The whole discrimination box is covered with .5 -inch wire 

 cloth, not shown in Fig. 1. The chamber C, and the near por- 

 tion of Ci and C4 are covered with black velvet paper which 

 prevents the bird from seeing the experimenter and the experi- 

 menter from seeing the bird until after the bird has discriminated 

 and hopped to either Ci or C4. 



(4) Experimental procedure. — Before beginning the experi- 

 ments each bird was left in the discrimination box for twenty- 

 four hours. All the doors were left open so that the bird could 

 thoroughly acquaint itself with the apparatus. The use of arti- 

 ficial light for illuminating the stimulus areas made it necessary 

 to conduct all the tests in a dark room. The birds were kept 

 in the dark room so that they would not be excited by being 

 moved from one room to another and also would become ac- 

 customed to the darkness and to the noise of the induction coil. 



A small electric light in the room was turned off during each 

 single test and then turned on again as soon as the bird had 

 made its choice of the stimulus area and passed on into the alley. 



On succeeding days (Sundays excepted) each bird was given 

 a series of 15 trials. A trial consisted in requiring the bird to 



