434 



Dr. W. Kiihne. On the 



activities, was the work of that everywhere predominant and distinctly 

 animal contrivance, the nervous system. 



In connexion with this, there seems to have arisen the view of the 

 ubiquity of nerves, that is, of so fine a penetration of the parts with 

 nerve radiations that, especially in muscle, not the smallest particle 

 free from nerve could be demonstrated, a view which on the strength 

 of microscopic research is coming up again afc the present day in a con- 

 stantly new dress, and finds energetic adherents (10), but as we shall 

 see is to be refuted, especially by experiment. If we disregard this, 

 we shall find the tendency to consider only nerves as excitable, in some 

 degree founded on the differentiation which transferred automatism to 

 the nervous matter, robbing all the remaining tissues of irritability, so 

 that they only retained the faculty of reacting to the stimulated nerve 

 with which they were bound up. This was as much as saying it was 

 impossible artificially to replace the nervous stimulus, or that if we did 

 succeed, we were strictly imitating it, in which case, indeed, we should 

 have come unawares upon the solution of the problem of motor 

 innervation. Against such arguments it availed nothing to point out 

 the excitability of nerveless sarcode, as was often done in favour of 

 irritability : for, just as it was formerly useless, because the real 

 genetic connexion of sarcode and muscle was not known, so to-day it 

 would have to be rejected, because automatic protoplasm can also be 

 correctly considered nervous. 



A non-irritable muscle would strike us as strange enough, and, 

 against all expectation, different from the nerve, when we consider 

 that the nerve-fibre, although incapable of being affected by all the 

 natural stimuli which excite its ganglion cells, free that is from auto- 

 matism, is artificially excitable at every spot by the most different 

 agents. However, we have no further need of such considerations, 

 since the question of irritability lies within a region where instead 

 of speculation, observation and experiment have become decisive. 



As a matter of fact, the older statements, long considered a good 

 basis for opposing irritability, are incorrect, as for instance, that an 

 excised piece of muscle in which no nerves could be seen with the 

 lens did not twitch on stimulating it. 



We can show you a little piece 3 mm. long from the end of the 

 sartorius muscle of the frog, in which the best microscope discovers no 

 traces of nerves, easily made recognisable by osmium- gold staining 

 (fig. 1). Such a piece, transversely cut off, twitches as we know at each 

 effective muscular stimulus. Pieces which can be obtained free from 

 nerves from many other muscles, behave in the same way, as for 

 instance pieces from the delicate muscles of the pectoral skin of a 

 frog (fig. 2). 



Further, the assertion was incorrect that everything that excited 

 the nerve made the muscle twitch, and vice versa ; for we see here a 



