C. ESTABLE 333 



contacts that are anatomically similar to those known to be functional. As men- 

 tioned in the text, we have indirect evidence that in some instances they do operate 

 (e.g. in cerebellar cortex or retina, in invertebrate ganglia). 



EccLES. I readily agree that at the crossing of two fibres there can be a iunctional 

 contact providing there is chemical secretion from one and chemical receptivity on 

 the other. 



EsTABLE. The electronmicroscope has not shown in cross-synapsis microvesicules 

 or mitochondria. That does not necessarily mean that a chemical mediator is 

 absent but, at the same time, it certainly does not suggest its presence : but, can we 

 be too dogmatic as to the necessity of a chemical mediator for contacts to be 

 operant? 



Gerard. One of the main points in your summary was the relation oi reciprocal 

 or irreciprocal conduction to symmetrical or asymmetrical contacts. This is, of 

 course, fully consistent with many physiological and model experiments and it may 

 interest the group to recall first the experiments Lillie did with his iron wire model. 

 He covered most of the wire with a glass tube, leaving two ends sticking out for 

 different lengths. He excited the model by scratching one of these. The large one 

 would cause the small one to respond, by currents through the wire and the 

 medium; but the small one would not excite the large one. This is asymmetry in 

 structure and in action. With equal sizes, this was always symmetrical activation. 



A more direct biological experiment was done by compressing the parallel 

 fibres at the middle of the sartorius muscle with a block of wood. If the muscle was 

 squeezed symmetrically conduction block occurred from either end to the other; 

 but if it was squeezed asymmetrically it was possible to get conduction in one 

 direction but not in the other. Of course, this fits with the emergence of activity 

 from the cell body into the axon and not always in the reverse direction, and main- 

 other experiments m the central nervous system at least seem to fit well with the 

 kind of valve phenomena that have been demonstrated peripherally, such as the 

 bouncing back of impulses from a cut cord. So that all in these cases Dr Estable's 

 thesis is supported; and it seems to me it would be hard to justify any dogmatic 

 statement that irreciprocal transmission can occur only when specific neurohumours 

 are present; they could hardly be present in most of these instances. 



EcCLES. I don't wish to be on record as dogmatically asserting that electrical 

 transmission does not occur in the vertebrate nervous system, but I will go on 

 record as saying that no experiments so far have shown that it does occur in an 

 undamaged C.N.S. Possibly the dorsal root potential and the Toennies reflex of 

 Vertebrates are due to electrical synaptic transmission. Elsewhere, when we have 

 studied cells intracellularly and investigated them in detail, we would surely have 

 recognized electrical transmission of the type described by Furshpan and Potter 

 with some crustacean s\-napses. There is no evidence whatsoever that such electrical 

 transmission does occur in the cells that have been investigated in this way. 



Fessard. I wish Dr Estable would clear up a point that has considerably troubled 

 me. I mean his statement that the same neurone could send an axon branch to the 

 radial fibres and another to the circular fibres of the iris ; that is to say, it could 

 elicit mydriasis and myosis at the same time. This sounds rather strange to me. 



Estable. Yes. 



Fessard. Have you good proof for that? It is certainly very disturbing. 



Estable. One can see in the iris of the penguin, whose iris is striated, axons 



