GERARD: NERVE METABOLISM AND FUNCTION 593 



actions on the nervous system; and so on. Thiamin is reported^^"^^ 

 to affect ACh action and synthesis and to be hberated from pre- 

 cursor in relatively large amounts from stimulated frog nerve even to 

 be the transmitter. Cocarboxylase, like ChE, is concentrated in the 

 nerve membrane.®- (For discussion of further recent evidence, see 

 Gerard and Libet.") I do not see how we can reasonably select the 

 ACh system from all this welter and just assign to it an essential role 

 in conduction of the nerve impulse. 



THE PROBLEM OF JUNCTIONAL TRANSMISSION 



In the time available, the problem of junctional transmission, pre- 

 sented mainly by Eccles, can only be touched upon, and even so the 

 case of autonomic effectors, the classical one of neurohumoral action, 

 which has not been before us, will be omitted. As for the neuro-myal 

 junction, the unquestioned facts, that ChE is more concentrated there 

 than elsewhere in the muscle fiber by a factor of 10* (Nachmansohn), 

 and that this region is more sensitive to added ACh by a similar factor 

 (Kuffler), are impressive; along with the potentiating and prolonging 

 action of eserine, long known for junction as well as ganglion. I am, 

 personally, less convinced of a transmitter role of ACh at the junction 

 than I was a few years back, but do not consider that the evidence is 

 crucial in either direction. (The observation®^ that the lizard muscle 

 fiber can respond to nerve stimulation at a time when ACh applied 

 to the end-plate is ineffective, although such ACh does cause contrac- 

 tion when first administered, has not been explained. Also, the end- 

 plate potential, often supposed to be set up by ACh liberation, is pres- 

 ent in invertebrate, as in vertebrate, muscle; but the end-plate region 

 in the former is not sensitive to ACh or to curare.®*) Discussion here 

 has been mostly on central synapses, and the reader should consider 

 these. 



As elaborated by Eccles, the currents that flow between an active 

 fiber region and an inactive one, whether in the same or another unit, 

 do account for the usual activation phenomena. The results of Ar- 

 vanitaki-* and of many other recent experimenters®^' ®®' ®^ show that 

 threshold changes and transmission from unit to unit in simple sys- 

 tems are accurately and quantitatively explicable in terms of the meas- 

 ured currents and the known geometry. Whether Eccles' detailed anal- 

 ysis of the situation at a synapse will hold up as well with time as he 

 was able to defend it here, we do not know, but there is every reason 

 to push such thinking further. (Some difficulties are: the very variable 

 structures which are found in synapses, where the two units may meet as 



