282 HARVEY CARR 



nected with their greater variability and erraticness. Blind 

 rats are rather difficult to keep in good physical condition. 

 They are more inclined to sluggishness in behavior, their appe- 

 tite is frequently diminished, their hair becomes dry and rough, 

 and they are sometimes rather flabby and cold to the touch. 

 I have also noted what may be termed as a " breakdown," of 

 which a number of examples may be cited. A group of six nor- 

 mals had been employed for four months in a sound discrimi- 

 nation experiment. Their conduct was normal and their physi- 

 cal condition was excellent at the conclusion of the experiment. 

 These animals were now blinded and given the maze problem. 

 Four of these rats proceeded to learn the maze in a normal 

 manner for a number of trials and then suffered the ' break- 

 down." They made complete failures of their attempts, became 

 exhausted before success was achieved, and finally refused to 

 run when placed in the maze. The break came on suddenly 

 and occurred between the 6th and the 15th trials, — after the 

 maze had been pretty well mastered. In another group of four 

 animals without previous experience, one rat made rapid prog- 

 ress up to the 12th trial and then refused to run. The break- 

 down may occur at almost any stage of the experimentation. 

 I had one individual that refused to run in the first trial. Another 

 rat broke down on the 142nd trial during the control tests, — 

 long after the maze had been mastered. Sometimes the rats 

 simply quit and refuse to work further. Others work indus- 

 triously but fail to find the food box, and are finally forced to 

 cease their efforts through exhaustion; this behavior may be 

 repeated in a number of successive trials until the rat quits 

 and refuses to work when placed in the maze. Recovery from 

 these breakdowns is rare and the rats may as well be eliminated 

 from the experiment. I have tested such rats for a number of 

 days in succession, and once a week for a couple of months in 

 the hope that an interval of rest would induce recovery. These 

 animals may continue to live and enjoy the average of health 

 for blind rats. Some have been kept in the laboratory for five 

 to six months. I have had some females bear and rear young 

 subsequent to the breakdown. The phenomenon needs extended 

 and systematic study. 



The above differences in the comparative data obviously must 

 be explained and interpreted in terms of vision. Certain con- 



