CEREBRAL FUNCTION IN LEARNING 67 



Determination of the extent of the lesions 



At the end of the experiments the animals were killed with 

 ether and their brains removed, fixed in 15 per cent formalin, and 

 imbedded in celloidin. Horizontal sections, 50/* in thickness, 

 were cut and each fifth section was kept for study. The sec- 

 tions were drawn in outline under a projection microscope and 

 the details of the lesions were filled in under higher power, 

 free hand. Owing probably to impurity of the alcohol used for 

 dehydration the sections proved unusually resistant to stains 

 and it was not always possible to make out cell details in them. 

 For that reason, only areas in which the destruction of the cortex 

 was obvious, as by complete absorption or by absolute separa- 

 tion from the remainder of the brain, were recorded as lesions. 

 The lesions recorded represent therefore the minimal extent 

 of injury; much larger areas than those indicated were almost 

 certainly rendered nonfunctional by the section of their sub- 

 cortical connections. 



From the drawings of the sections the dimensions of the 

 lesions were transferred with proportional dividers to correspond- 

 ing levels on the diagrams of the brain, the points so determined 

 were connected by lines, and the injured areas thus plotted 

 were finally inked in. The method permits of some error, 

 owing to disproportion between the sections and the diagrams, 

 but it seems accurate enough for the present purpose. In 

 addition to the diagrams of the dorsal and lateral aspects of 

 each injured hemisphere a detailed camera drawing of one 

 section was prepared. This was selected in the plane of the 

 thalamus and lateral ventricles wherever possible. Because 

 of limited space for reproduction these figures of sections had 

 to be made somewhat diagrammatic. The degenerated cortex 

 is indicated on them in solid black (plates 1, 2, and 3). 



