Causation of Vital Movement. 



441 



Nerves end blindly in the muscles ; as a rule they are not even finely 

 pointed, and still less do they spread out diffusely in such a way as 

 might make the true ending difficult to find. They end quite dis- 

 tinctly. But the ends always lie beneath the sarcolemma, in such a way 

 that no foreign tissue intrudes between them and the muscle, so that 

 what is fluid in the muscle can directly moisten the nerve. The sub- 

 lemmal nerve is clothed with nothing else than the axolemma. The 

 nerve never penetrates into the depths of the muscle substance ; on 

 the contrary, it remains confined to the sublemmal surface of the 

 contractile cylinder or prism. Each nerve end consists of several 

 branches, like antlers, arising by division, which together form the 

 terminal nerve-branch. Apart from the form of the antlers, this short 

 description is exhaustive for many animals, since neither in the sub- 

 lemmal nerve need any special additional structures occur, such as 

 nuclei, nor any kind of modification of the muscle substance in the 

 field of innervation. There is much to indicate that the nerve-fibre 

 proper, or axis-cylinder, does not change its constitution in passing 

 through the sarcolemma, still it is to be remarked that the twigs of 

 the terminal branches, although as long as they live often apparently 

 longitudinally striated, have not yet, even in the most favourable 

 stainings, been found to present the general fibrillar structure of 

 nerves. 



According to these results of morphological research, it appears 

 that contact of the muscle substance with the non-medullated nerve 

 suffices to allow the transfer of the excitation from the latter to the 

 former. The only strange thing is that in reversed order excitation 

 of the muscle never extends to its own nerve. This is still stranger 

 because, according to Matteucci's well-known discovery, a foreign 

 medullated nerve simply laid upon the muscle is powerfully excited by 

 the contraction — so powerfully that the smallest contracting muscle 

 barely touching it in more than a mere point excites the strongest 

 nerve, while, on the other hand, we never see muscles excited by 

 nerves which are merely pressed against them. 



In the investments, then, of the nerve and the muscle substance 

 appears to exist one of the elements which admits the neuro-muscular 

 excitation exclusively to the field of innervation, and among those 

 investments it need not be the medullary sheath. The delicate 

 membranes of the sarcolemma and neurilemma suffice, for muscle 

 cannot be excited by superimposed w<m-medullated nerves. At any 

 rate, I have tried in vain to excite muscles by the most intimate 

 contact of the fine terminal ramification of the optic nerve in the 

 retina or the n. olfactorius from the pike, or even the delicate nerves 

 of Anodonta, by stimulating these non-medullated nerves. 



If we imagine the activity of the nerve to start with a chemical 

 process, and that a chemical stimulant, as du Bois-Reymond (19) once 



VOL. xliv. 2 K 



