FUN DA MENTA L " LA WS " OF NERVE-A C TION. 189 



These several facts form a group of ideas in which the 

 connecting consideration may be brought out and expressed 

 by saying that, by virtue of the anatomical interruption of 

 continuity, the anterior cornual cell plays the part of a 

 nerve-valve — permitting the passage of nerve-impulses in 

 a centrifugal direction, obstructing them in a centripetal 

 direction — and that the interruption is a determining factor 

 as regards Wallerian degeneration of nerve-fibres. De- 

 generation occurring below i and 2 is in no known relation 

 with the fact that their tract is efferent, 1 but is in accord- 

 ance with the fact that the part below py is not in proto- 

 plasmic continuity with any cell, while the part below m is 

 in protoplasmic continuity with an anterior cornual cell 

 ("trophic"). We may understand better from this point 



known grounds upon which the same conclusion had been based, and 

 place it upon the extremely insecure basis of their own electrical experi- 

 ments, presenting it as a surprising discovery, and linking it in a curiously 

 confused way with psychological theories concerning kinaesthesis. They 

 find, moreover, or infer, that centrifugal as well as centripetal impulses can 

 pass down the posterior roots, and apply this "fact" in a similar manner 

 to support their views of kinresthesis (Gotch and Horsley, Phil. Trans. 

 R. S., 1 891. Croonian Lecture, p. 509). For a criticism of these views 

 see Waller, "On the Functional Attributes of the Cerebral Cortex," 

 Brain, p. 384, 1892. 



1 The misconceptions still prevailing as to the fundamental facts of 

 degeneration, as expressed in recent and authoritative text-books of Ana- 

 tomy and of Physiology, are survivals or sports that are very difficult to 

 account for. " The pathological method depends upon the trophic influence 

 exercised by nerve-cells. It is found that every nerve-fibre must receive a 

 certain influence from a nerve-cell in order to benefit by the lymph with 

 which it is surrounded. This is called trophic influence. The trophic 

 cells for the sensory fibres are situated in the ganglia in the posterior 

 roots ; hence if the roots be divided between the cord and the ganglia, the 

 nerve-tracts degenerate in an upward direction, and the degenerated tracts 

 can be seen surrounded by the unaffected tracts. Ascending degeneration is 

 therefore characteristic of centripetal tracts''' (Morris' Anatomy, 1893). This 

 being precisely what is not the case. When a nerve trunk is cut across, the 

 degeneration actually descends, in the sense that the progress of the de- 

 generative changes may be traced downwards ; they begin at the section 

 and travel downwards at a rate sufficiently slow to permit a difference being 

 observed between the progress of degeneration at a spot near the section 

 and that at one farther off (Foster's Physiology, 5th ed., 1890, p. 871). 

 Which is a very graphic description of what does not occur. 



