Causation of Vital Movement 

 Fig. 5. Fig. 6. 



437 



connected only by means of a very short tendon, the so-called inscrip- 

 tion, which passes completely through the muscle (ii in fig. 5), so 

 that it really consists of two muscles. If the nerve common to both 

 is stimulated at any point, then both parts of the muscle contract, but 

 if the muscle substance itself is stimulated, then the contraction 

 travels no further from the place where the stimulus was applied than 

 to the limits of continuity of the muscle-fibres. 



The power of motor nerves to conduct in both directions is cer- 

 tainly of general significance in regard to the inner mechanism of 

 nerves, but we have only approached it here, because it was necessary 

 for the decisive proof of muscular irritability, as obtained in our last 

 experiment with the m. gracilis. Whenever a muscle is provided with 

 a nervation and branchings of the separate nerve-fibres like that of the 

 gracilis, some group of muscle-fibres can serve to indicate whether a 

 stimulus has affected this alone or the nerves lying in it as well. If 

 nerves are present at the point of stimulation, and if the agent was at 

 the same time a nerve stimulus, this is shown by the simultaneous 

 contraction of distant parts which are accessible by means of the 

 nerve's power of conducting in both directions. In cases where we 

 can see the coarser nervation, the indirectly produced contractions 

 can be predicted, and these form so certain a criterion of neuromus- 

 cular excitations that by them the presence of the finest nerves may 

 be proved, whose existence might otherwise be quite incapable of 

 proof by any other means, as, for instance, by the use of the micro- 

 scope. If these contractions are wanting, as was the case in our 

 experiments with the lower end of the muscle, we know that either 

 the spot stimulated is free from nerves, or that the stimulus employed 

 was ineffectual as to the nerves and affected the muscle substance 

 exclusively. In both cases then independent irritability is proved 

 for those muscle-fibres which were directly excited and contracted. 



