CEREBRAL FUNCTION IN THE RAT 77 



the knife can be more accurately determined, but slight varia- 

 tions cannot be avoided and these would make the lesions dis- 

 similar. In addition, the quantity and the extent of the hemor- 

 rhage cannot be controlled, and this hemorrhage acts as a super- 

 imposed lesion. In some cases the lateral ventricles were found 

 to be filled with blood, and in other cases clots were found at 

 the base and even at the cerebro-cerebellar junction. Mention 

 may also be made here of the variations in the location of the 

 stimulable areas (the motor areas), report of which will later be 

 made by one of us (L). Whatever operative technique is used 

 the destructions are varying, and the most that can be expected 

 in these small animals is to operate on sufficient numbers, and 

 to select and compare those cases which have relatively similar 

 lesions. This we have done. In all cases the lesions will be 

 described and the comparison of sets of animals will be made. 



When the experimental part of the work was completed the 

 animals were killed and their brains were removed, fixed in 10 

 per cent formaldehyde, dehydrated, and cut in celloidin. Hori- 

 zontal sections 80 M. in thickness were cut and every tenth 

 section was stained in toluidin blue and mounted in balsam. 

 Each brain was given an arbitrary number and the examination 

 and description of the lesions were made without knowledge of 

 the behavior data, except in the case of the extensive lesions 

 which were recognizable in the sections. 



For reconstruction of the lesions serial outline sketches of the 

 sections were made under the projection microscope to show the 

 extent of the lesion visible under low powers of the microscope. 

 The sections were then examined under higher power and the 

 parts which seemed certainly involved in the lesion, either 

 through actual destruction of the cortex or severance from all 

 connection with the descending fiber tracts, were filled in on the 

 sketches. The plane of the sections was determined for each 

 brain by reference to the corpora quadrigemina and knee of the 

 corpus callosum, measurements of the extent of the lesion were 

 made, and these were reduced to the dimensions of the diagram 

 used in case the brain varied from the average. Finally the 

 extent of the lesion was marked on the diagram in the planes of 

 the sections and the areas so outlined were blocked in. 



