170 



Croontan Lecture, 1906. — On Nerve Endings and on Special 

 Excitable Substances in Cells. 



By J. N. Langley, F.R.S., Professor of Physiology in the University of 



Cambridge. 



(Received and Read May 24, 1906.) 



Amongst the fundamental problems of physiology is the determination 

 of the actual seat of the changes which accompany or are the cause of 

 physiological activity. The earliest step was the attribution of the more 

 obvious functions of the body to the several organs which compose it. This 

 has been followed by more or less successful attempts to ascertain the 

 separate function of each tissue of an organ, and of each constituent of 

 a tissue. And in recent years investigation has been largely concerned with 

 the endeavour to localise functions long known, and those which from time 

 to time are discovered, in the several parts, and in the several chemical 

 constitutents of the ultimate unit, the cell. 



I propose to-day to consider what is the actual seat of certain physiological 

 activities in cells, and chiefly in those of muscular and nervous tissues. 

 About 50 years ago Claude Bernard investigated the action of various 

 poisons on the properties of the nervous and muscular systems. The main 

 conclusions which he drew are still almost universally accepted. The most 

 important observations were those on the action of curari. It had long been 

 known that a muscle contracted when it was stimulated, but it was a 

 question of interminable argument whether it responded to the stimulus in 

 virtue of its own intrinsic properties, or in consequence of the presence 

 of nerve-fibres in its substance. 



Bernard discovered that after a small amount of curari had been adminis- 

 tered to a frog, the motor nerves of the muscles of the trunk and limbs were 

 no longer capable of causing contraction, but that the muscles contracted in 

 the usual manner when stimulated directly. Assuming that the nerve-fibres 

 in the muscles were as incapable of causing contraction as those outside 

 them, it followed that the muscles are excitable in themselves, apart from 

 any nervous impulses, and thus the first piece of fairly satisfactory evidence 

 was obtained that muscle is not only contractile but irritable by other 

 agencies than its nerves. Bernard* also showed that curari in the amount 



* Pelouze and Bernard (' Comptes Rendus Acad. d. Sci.,' 1850, p. 533) were the first to 

 point out that stimulation of the nerves bad no effect in a frog to which curari had been 

 administered. Bernard continued the investigation of the action of curari, and gave the 



