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BRAIN MECHANISMS AND LEARNING 



is the exclusive outlet for neuronal influence and acts only by way of its 

 terminal portion, this being a generalization of what occurs at the level of 

 better studied synapses, in the cord and neuromuscular junctions. Numer- 

 ous electrophysiological facts and the discovery of specific chemical 

 mediators released at the axon endings supported the thesis that neurones 



Fig. 5 

 Dendro-dendritic and dendro-soniatic contacts. Photomicrographs of albino rabbit 

 retina demonstrating dendro-dendritic and dendro-somatic synapses between 

 horizontal neurones. D.s.d. syn. shows a dendrite establishing relationship with body 

 and prolongations of neurone D; D.s. syn. is a synapse between the dendrite D. and 

 the soma of neurone P. (Cajal's silver method.) 



do act by these terminations. The statement that a neurone acts upon 

 another through its axonic extremities cannot be gainsaid, but one should 

 be careful not to infer that no other possible manner of interneuronal 

 induction can exist. 



Numerous investigations in recent years have shown the existence in 

 the C.N.S. of Vertebrates and Invertebrates of the following contacts 



