574 Stewart Paton 



tlie cord, eluse to the exit of tlie ventral roots or in the span be- 

 tween the cord and niyotome. About tlie same time, or in some 

 eases slightly jireceediui;- it, neurofibrils ap|)ear in the processes of 

 the large cells of Beard close to the nucleus. 



The ajtpearauce of neurofibrils may generally be considered to 

 be an indication that physiological activity has already actually 

 begun, or will soon begin in the tract in which they have beeu 

 differentiated. 



It seems to be not at all iniprobable that Impulses, centrifugai 

 as well as centripetal in origin, may pla\' an important part in the 

 differentiation of the neurofibrils (neurofibrillation). 



The opinion held by a number of investigators that the neuro- 

 fibrils are to be regarded merely as forniiug part of the supporting 

 substance in the nerves and nerve cells is apparently not substantia- 

 ted by the facts. The important hearing they have to function, as indi- 

 cated by x\pÄTHY, Bethe and others, seems to be coufirmed by the follow- 

 ing observations. a) Neurofibrils first appear in the tracts which are the 

 earliest to give evidence of functional activit3^ b) In the nerves, in well 

 stained specimen?, it may be seen that the neurofibrils appear as 

 attenuated delicate structures running lougitudinally in the axis 

 cylinder without cross counections. c) Their intimate connection with 

 the neuroblasts, at a time when the spongioblast Clements consist 

 only of a small body and an attenuated process which generally 

 bifurcates in or near the outer marginal veil without giving off 

 fibrils of any description. In order to prove that the neuro-reticulum 

 in reality serves the purpose of a supporting structure, it must first 

 be shown that the net is the product of spongioblasts, and of this 

 thcre is not the slightest evidence. d) The neurofibrillation begius 

 in and about the cells which first become functionally active and 

 spreads from this point as a centre. The ventral hörn cells in the 

 cord afford an excellent example of this fact. There the neuro- 

 reticulum begins in the outer layers of the cord or in the plas- 

 modesmata and creeps inwards towards the spongioblasts and central 

 canal and never grows in the opposite direction, e) The majority 

 of the bundles of fibrils forming the posterior root fibrils first make 

 their appearance in the spinai ganglia. f) Coarse thick fibrils 

 which eventually split longitudinally are seen at a very early period 

 in the outer marginai veil of the cord. The only cells with whieh 

 these are connected are those lying within this same zone and 

 possessing ali the characteristics of neuroblasts. g) The very re- 



