374 K. LISSAK, E. ENDROCZI AND E. VINCZE 



the reticular formation and the amount of fluid introduced varied between 

 0-01 and 0-05 ml. It was observed that the brain extract strengthened the 

 labile processes of diff"erentiation, and shortened the duration of latency. 

 GABA or GABOB, even in concentrations of 1-10 mg/01 ml, failed to 

 produce changes in the conditional reflex processes. 



In summary it may be stated that the brain tissue contains a substance 

 whose physicochemical properties, as revealed by paper chromatography, 

 resemble those of GABA. However, the two substances differ in their effects. 

 On the one hand, the natural inhibitory substance is more pronounced in its 

 effects ; on the other, it will act on receptors on which even high concentrations 

 of GABA are ineffective. The basis of this disparity may be an essential 

 difference in structure. Or the natural inhibitory substance might represent a 

 more complex compound of GABA, which differs in permeability or has a 

 more pronounced biologic action. 



In order to be able to form a final view of the mediation of inhibition it 

 would be necessary to have a more definite knowledge of the essential 

 properties of the inhibitory factor and the morphologic substrate through 

 which it acts. 



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