386 BRAIN MECHANISMS AND LEARNING 



logically to the nucleic acids and, for events which are primarily cytoplas- 

 mic, to the ribonucleic acids. 



Ribonucleic acid stains (methyl green pyronin method) have been done 

 on sections through the region of the mirror focus in nine animals after 

 preliminary electrical studies had clearly indicated the extent and distribu- 

 tion of both primary and secondary discharging areas. Control sections 

 were taken from electrically uninvolved areas of brain and, in addition, 

 every third section was treated with ribonucleasc to insure that the sub- 



FlG. 1 I 



Higher pi) werphntoinicrogrdph denumstrating the characteristic concentration 

 of pyronin positive material along the inner surface of the membrane. The 

 stained material extends far into the dendrite. Note also the appearance of a 

 bilobcd nucleus Methyl green pyronin stain. Magnification ■ 840. 



Stance stained was ribonucleic acid. Fig. 9 demonstrates a small nest of 

 darkly stained cells surrounded by the more lightly coloured regions of 

 normal cortex. Such densely stained cells were consistently found in 

 areas coincident with the electrically defined mirror focus. A slightly 

 higher power photomicrograph (Fig. 10) illustrates the penetration of the 

 pyronin-positive material into the dendrite and also indicates the wedge- 

 like distribution of the stained cell system. Pigmented cells extend through- 

 out the depth of the cortex. At still higher magnification the extent of 

 penetration into the dendrite is clearer (Fig. i 1) and one may observe a 



