STUDIES OF CEREBRAL FUNCTION. IX 15 



Surgical and anatomical methods 



The methods of destroying the cerebral cortex were those 

 previously described by Lashley ('29), with operation in two 

 stages for the more extensive lesions. Since we wished to 

 obtain four groups of animals with similar lesions, we oper- 

 ated on not less than four animals at one time, attempting 

 to duplicate the lesions in all and distributing them later to 

 the four groups. At the time of operation a sketch was made 

 of the type of lesion, and in case a member of the group died, 

 it was replaced by another with duplicate operation. 



The method of reconstruction of the lesions was that de- 

 scribed earlier: graphic reconstruction of serial sections 

 (Lashley, '29 ). 4 We have paid especial attention to the sub- 

 cortical lesions, which cannot be avoided with larger destruc- 

 tions of the cortex. Analyses of the data to determine the 

 influence of subcortical injuries upon the results are reported 

 on page 32. 



Graphic and statistical analysis 



The diagrams prepared in reconstruction of the serial sec- 

 tions represent approximately the surface distribution of the 



*Loucks ('32) has recently advocated a method which differs from the above 

 in three particulars: the use of a fiber stain, the arbitrary limitation of the 

 boundary of the lesion at the point where total destruction of tissue cuts the 

 pyramidal layer of the cortex, and the measurement of the lesion along the 

 perimeter of each section, instead of surface area of the reconstructed diagram. 

 These differences in method do not seem to us advantageous. Although in old 

 lesions there is usually a clean-cut destruction of tissue, the cortex bounding 

 the area of completed destruction often shows pathological changes which cer- 

 tainly render it non-functional. Fiber stains do not reveal this and the arbitrary 

 criterion of complete destruction disregards it. In determining the extent of 

 lesion we have drawn the boundaries at the point where the cortex assumes a 

 normal appearance, providing against personal bias by having the observer 

 in ignorance of the animal's training record when the reconstruction of the 

 lesion is made. 



The method of measuring the lesion along the perimeter of the section is 

 doubtless somewhat more accurate than the determination from the graphic recon- 

 struction. Some years ago, the senior author made a number of determinations 

 by both methods. The difference in results by the two methods was about 5 per 

 cent, which was within the limits of accuracy in remeasurement by either method. 



