290 HARVEY CARR 



the normal animals learn to utilize visual stimuli as controls in 

 selecting the true path from the numerous cul de sacs. b. Vision 

 may be advantageous because of the tonic effect of light. Visual 

 stimuli exert a tonic and stimulative effect upon the various 

 activities of the organism. Rats with vision exhibit the greater 

 vigor and superabundance of bodily activity. Surplus activity 

 is necessarily valuable in any trial and error mode of learning. 

 This effect of light will also be manifested by the vital activities. 

 Heightened vitality will be influential via of an increased reten- 

 tive capacity or a stronger hunger motive. Decreased activity 

 and vitality resulting from loss of vision may interact upon each 

 other; decreased activity, or lack of exercise, will lower the 

 vital tonus of the organism, and this lowered vitality will in 

 turn produce sluggishness of behavior, c. We may assume that 

 the learning capacity of blind rats has been minimized by cer- 

 tain deleterious effects of the operation per se r The connection 

 between these effects and learning capacity may be conceived 

 in several ways. The operation (the surgical shock or the effect 

 of the ether) may act directly upon the vital activities and thus 

 influence learning capacity as sketched above. The organic 

 aftereffects may be conceived as some sort of a nervous irritant 

 which operates as a distractive stimulus and thus produces erratic 

 and exaggerated behavior. Likewise the effects may be nervous 

 modifications of such a character as to render the animal more 

 susceptible than usual to any novel stimulative conditions. The 

 animal is thus prone to erratic, irregular and exaggerated modes 

 of response detrimental to the mastery of the maze. On this 

 hypothesis, stability and instability will characterize normal 

 and blind rats respectively. 



The last two hypotheses are supported by several lines of 

 evidence. Blind rats frequently exhibit signs of decreased 

 vitality such as muscular flabbiness, rough coats, poor circula- 

 tion, poor appetite, and a susceptibility to disease. Blind 

 animals are also less active as a general rule; the normal vigor, 

 persistence, and superabundance of activity is frequently lack- 

 ing. The phenomenon of breakdowns characteristic of blind 

 rats also suggests the validity of the third conception. The 

 greater erraticness and variability of blind animals, — the ten- 

 dency to make now and then unusually large error scores, is 

 explicable in terms of the third conception. There are no facts 



