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



that they act on nerve endings. But the possibility of an intermediate view 

 must be mentioned. There are some observers who consider that nerve and 

 muscle are continuous, and it is conceivable that a certain region of the 

 junction should belong to both nerve and muscle in the sense that either 

 could keep it alive. The special properties attributed to the nerve ending 

 might then be attributed to the junctional region, half muscle and half 

 nerve. With regard to this, it will be noted that the junctional region, if it 

 exists, must be in the muscle, since we have good reason to believe that all 

 the visible nerve ending degenerates on section of the nerve. 



In the simplest case, that of the nerve endings of amphibia, the substance 

 which has been described as continuous with the endings is clearly the 

 sarcoplasm of the muscle, which stretches throughout the muscle fibre, and no 

 substance of distinct histological characters which could be regarded as a 

 junctional substance is shown by the microscope. 



In the end plate form of nerve ending there is it is true the specially 

 modified sarcoplasm which forms the " sole." But, as was shown by Kiihne, 

 some of the hypolemmal fibres commonly run past the limits of the sole. 



But the theory of continuity seems to me to have the balance of evidence 

 decidedly against it. As Kiihne* pointed out in a previous Croonian Lecture, 

 the properly stained hypolemmal fibres terminate usually in rounded ends 

 sharply marked off from the muscle substance, and every method which 

 brings out the nerve endings clearly, brings out this characteristic. The 

 outline of a hypolemmal fibre is as distinct at its end as it is in its pre-terminal 

 course. In the case of typical nerve endings, it is only when they are viewed 

 in all the indistinctness of the fresh specimen, or are made granular by treat- 

 ment, that any appearance of continuity is suggested. 



Kiihne has also pointed out that excitation of the muscle substance does not 

 cause a stimulus to pass back through the nerve ending, and this might 

 reasonably be expected to occur if there were continuity. 



The chief observations in favour of continuity are those on the development 

 of the nerves in the embryo.f As I have said elsewhere, if it were shown 

 that continuity exists in the early embryonic state, it would not follow that it 

 continues to exist in later stages. With differentiation of function, histological 

 separation might well take place.*. 



* Kiihne, ' Koy. Soc. Proc.,' vol. 44, p. 427, 1888. 



t For a critical account of these observations, cf. Kolliker, 'Zeitsehr. f. wissensch. 

 Zool.,' vol. 82, 1905. 



% Since the above was written, a paper has been published by Pfliiger (' Arch. f. d. 

 ges. Physiol.,' vol. 1 12, p. 1, 1906), in which he upholds the theory of continuity. It is a 

 measure of the need for further investigation that the well-known observations on the 



