10 K. S. LASHLEY 



4. Control of reaction to odor, a) Food odors. Both alleys 

 from the discrimination compartment communicated simi- 

 larly by small doorways with compartments containing food. 

 These were always closed by light swinging doors of mica 

 which the animal must open to enter the food compartment. 

 h) Ozone from the punishment grill. As the box was ar- 

 ranged the grills were not charged until after errors were 

 made. 



5. Control .for reaction to sound. The box was adjusted 

 before the animal was brought from the home cage in another 

 room. Correct discrimination was evidence that the animal 

 was not reacting to the noise of setting the box. 



6. Accidental cues from experimenter. Trials given by 

 another person without disturbing discrimination controlled 

 such accidental cues. 



This series of tests is time-consuming and tends to break 

 down the discrimination habit, since any slight change in the 

 total situation disturbs the animal. Tests 1 and 2 were there- 

 fore made only with every fifth animal, the entire series with 

 about one in ten. In no case was evidence obtained that the 

 animal was discriminating on the basis of any stimuli other 

 than the visual ones. Whether the reaction was to the retinal 

 image of the lamp or to the general illumination of the ap- 

 paratus was not determined. From the behavior of the ani- 

 mals and from tests made earlier (Lashley, '12) it is probable 

 that both elements enter into the reaction. 



Surgical and histological methods 



Operations were performed with thermocautery under 

 ether anesthesia. The lesions were restricted to the occipital 

 third of the cortex, both hemispheres being injured in every 

 operation, sometimes symmetrically, sometimes not. The ex- 

 tent and form of the injury was left largely to chance, 

 although an effort was made to destroy every possible part 

 and combination of parts of the occipital cortex in one or 

 another animal. 



