190 H. M. JOHNSON 



THE ANIMALS USED 



The four animals used in the present study were described 

 in the earlier report just cited, and were therein designated 

 severally as Dog 1, Monkey 2, and Chicks 1 and 2. Dog 1 

 failed to learn the problem. This experiment is a part of a 

 special study of that animal's vision. His results are interesting 

 only when considered in connection with those obtained in the 

 other work, so I shall reserve them for a separate report. 3 Chick 

 1 also failed to learn the problem in 800 trials. He had a large 

 refractive error (1.5 D. hyperopia) in the right eye, and was 

 also very easily excited by punishment or by unusual noise, 

 so that he would refuse to work in the experiment -box. Event- 

 ually he was blinded in the left eye during a fight, and I did not 

 resume experimentation on him. On account of lack of space 

 I shall not include his daily records in this report. Chick 2, 

 both of whose eyes were emmetropic, had distinguished as 

 striate a system each member of which was 0.78 mm. wide at 

 a distance of 60 cm. from the eye; the width under threshold- 

 conditions for Monkey 2 being 0.163 mm. at the same distance. 

 Chick 2 had also yielded a difference threshold for width of visi- 

 ble striae of 33% to 42%, and Monkey 2, a series of thresholds 

 as low as 3% under optimal conditions. 



In the course of the work some serious interruptions occurred. 

 In September, 1914, Chick 2 acquired a severe white diarrhoea, 

 and became greatly weakened. He finally refused to eat, and 

 all the masculine characteristics of his behavior disappeared. I 

 transferred him to an out-door yard where he had plenty of 

 range. He showed improvement in a few days, and made a 

 complete recovery in three months. Meantime his comb grew 

 very large and depended over the left eye, largely occluding 

 the visual field on that side. I amputated the comb March 6, 

 1915, and resumed retraining on the 10th. On the 20th he 

 became engaged in a fight and was nearly killed. Other uncon- 

 trollable conditions then intervened and prevented the resump- 

 tion of work until June 16, 1915. 



Monkey 2 — a frail and probably tubercular little animal — also 

 sickened May 21, 1915. He refused food and in two days be- 

 came too weak to stand alone. I moved him to a room where 



3 Johnson, H. M. Visual pattern-discrimination in the vertebrates. V. A demon- 

 stration of the dog's deficiency in detail-vision. To appear in this journal. 



