302 HARVEY CARR 



of the maze. Anosmic animals learn the maze as readily as do 

 normal rats. The olfactory operation produces no deleterious 

 effect upon the vitality or behavior of the animals. The elimi- 

 nation of vision slightly decreases learning capacity, but this 

 effect is limited to certain individuals; the vital capacity of 

 certain rats is also lowered. The combined loss of smell and 

 vision exerts some effect upon vitality, but this effect is apparently 

 no greater than that resulting from the loss of vision alone. The 

 combined loss of the two senses results in a pronounced decrease 

 in learning capacity, an effect which can not be regarded as the 

 arithmetical sum of the results of the two operations taken 

 separately. 



These facts indicate that the diminished vitality and learning 

 capacity of the blind animals and the blind and anosmic groups 

 can not be due to any effects of the operation per se, such as 

 surgical shock, ether effects, etc. The anosmic operation is 

 much more serious and difficult than the optic one, and any 

 operative effects should be more evident and more extensive 

 in the anosmic than in the blind groups. The reverse situation 

 obtained; the anosmics were not affected while many of the 

 blind rats were. The combined operation for the two senses 

 is not any more prolonged or severe than for smell alone. If the 

 operative effects are' responsible for the deficiencies of learning 

 capacity, one should expect as good records from the blind and 

 anosmic groups as from the anosmic animals; as a matter of 

 fact the anosmic animals suffered no deleterious effects while 

 the learning capacity of the blind and anosmic rats was far 

 below normal. 



In the previous paper we noted three possible ways in which 

 any sense might function in order to increase learning capacity. 

 Sensitivity may be advantageous because of either a directive 

 or tonic influence upon behavior and the vital activities. The 

 removal of a sense organ may be disadvantageous not because 

 of the elimination of sensitivity but because of certain deleterious 

 effects of the operation itself. The directive function of vision 

 for our conditions was decisively eliminated as one of the possi- 

 bilities. The data of this paper also eliminates the third hypoth- 

 esis. We are thus forced to conclude that the beneficial in- 

 fluence of vision upon learning capacity is due to the tonic and 

 stimulative effect of retinal stimuli. 



