182 Prof. J. N. Langley. On Nerve Endings and on [May 24, 



is rendered ineffective, we may explain on the supposition that the nicotine 

 muscle compound ceases to be irritable or conductive to nervous stimuli, 

 before the maximal combination with nicotine has taken place. The degree 

 of combination is essentially a question of the relative chemical affinities of 

 the radicle of the muscle substance with other radicles and with nicotine. 



It is true that, as mentioned earlier (p. 172), microscopic changes have 

 been described in nerve endings as the result of giving curari, but these 

 do not necessarily show a special action on the nerve ending. In the 

 instance described by Kuhne, the increase in distinctness in the nerve 

 endings of the lizard might equally well be due to an action on the " sole " 

 or muscular protoplasmic mass below the nerve ending. And with regard 

 to the observations of Herzen and Odier it is to be noted that the granular 

 changes found in the nerve endings after curari were also found in the axis 

 cylinders a variable distance up the trunk of the nerve, and it is certain 

 that the abolition of nerve effect, produced by small and by moderate 

 amounts of curari, is independent of any changes in the trunk of the nerve. 



Further, there is no certain histological difference between the nerve- 

 fibres before and after branching into nerve endings ; although some 

 differences have been described, the general evidence is that the nerve 

 endings are simply branches of the axis. 



The probability then, I take it, is that none of the phenomena of nerve 

 and muscle stimulation are due to a chemical difference between the axis 

 cylinder and the nerve endings, and in that case it follows not only that 

 the poisoning phenomena of a large number of drugs are due to changes 

 brought about directly in some constituent of the muscle, but also that 

 the peripheral fatigue usually attributed to changes in the nerve endings 

 is really due to fatigue of a special constituent of the muscle. 



Since neither curari nor nicotine, even in large doses, prevents direct 

 stimulation of muscle from causing contraction, it is obvious that the muscle 

 substance which combines with nicotine or curari is not identical with the 

 substance which contracts. It is convenient to have a term for the specially 

 excitable constituent, and I have called it the receptive substance. It 

 receives the stimulus and, by transmitting it, causes contraction. 



Beyond this we cannot go at present with any certainty. I may indicate 

 briefly one or two possibilities. 



It is well known that Bottazzi* has given reasons for the theory that 

 sarcoplasm is contractile, but that it contracts more slowly than the fibrillar 

 material. We might then refer the nicotine contraction to the sarcoplasm, 

 and the slowness of the contraction would imply that the fibrillaB are not 

 * Bottazzi, ' Journ. of Physiol.,' vol. 21, p. 1, 1897. 



