THOUGHTS ON INHIBITION IN THE SPINAL CORD 15 



by Graham (1935) there arose a process known in peripheral nerve that was 

 capable of accounting in large measure for the qualities of inhibition as 

 discussed by Eccles and Sherrington (1931) in relation to the flexor reflex 

 (Gasser, 1937). 



It is curious that Keith Lucas in stating his philosophical approach to the 

 problem did not consider as worthy of mention inhibition as a direct action 

 of peripheral nerve fibers, for the vagal inhibition described by the brothers 

 Weber was unequivocally just that. There is, in fact, not a single reference 

 to the Webers in his book The Conduction of the Nervous Impulse. 



The hypothesis of Keith Lucas, based on refractoriness and decremental 

 conduction, and that of Gasser, based on subnormality, were specific. It 

 could be held that those who believed in inhibition as a direct action had no 

 specific hypothesis to put forward — at least until Loewi (1921) demonstrated 

 the chemical nature of vagal inhibitory action. 



This brings us to consideration of another dichotomy of thought in which 

 so-called chemical hypotheses and electrical hypotheses were pitted each sort 

 against the other. I feel it should be made clear that the electrical and chemical 

 hypotheses refer to the mode of synaptic action by means of which inhibition, 

 or for that matter excitation, are brought about. They are thus aspects of 

 the hypotheses of direct inhibition. Hypotheses of indirect inhibition, except 

 for their aim of avoiding the necessity of postulating specifically inhibitory 

 synapses, are fundamentally clear of obligate statements as to the mode of 

 synaptic action itself, whether it be chemical or electrical. 



It is interesting that at the time Adrian (1924) wrote on "Some recent 

 work on inliibition" the important rivalry, if such it was, was between the 

 Verworn, Lucas and Adrian hypothesis of indirect inhibition by operation 

 of the Wedensky phenomenon and the "humoral theory", as Adrian called 

 it, based then on evidences of peripheral actions by chemical substances, 

 notably that provided by Loewi (1921). 



Through confusion in thought the various hypotheses of indirect inhibition 

 came to be called electrical hypotheses although, as 1 pointed out, they are 

 not necessarily anything of the sort. 



I think it would be correct to say that most electrical hypotheses of trans- 

 mission, and this includes inhibition in the synaptic action sense, have never 

 reached the dignity of publication. 1 think it would also be correct to say 

 that the major reasons for this were in the case of excitation to dispose of 

 the unwanted anodes and in the case of inliibition to dispense with the 

 unwanted cathodes. However, an exception was the electrical hypothesis of 

 Brooks and Eccles (1947) that inserted into the monosynaptic reflex inhibi- 

 tory pathway a subliminally acting interneuron which by generating a 

 synaptic potential would induce, it was supposed, an anelectronic area in the 

 motoneuron subjacent to the inhibitory knob. 



In as much as anelectrotonus now has been mentioned for the first time, 



