246 Ross Granville Harrison 



In view of these facts the observation of an increase in the number 

 of fibrillae in a given peripheral nerve as its end is approached can 

 have no w^eight in support of the hypothesis that some of them are 

 lacking connection with the center.^" 



There is another consideration which Braus takes up in sup- 

 port of his explanation of the greater thickness of the nerves within 

 the transplanted extremity. He says, if one follows the develop- 

 ment of the specimens until the nerves become myelinated, one 

 finds on counting the fibers that there are now no more within 

 the transplanted limb than in the connecting nerves. This shows, 

 it is maintained, that, of the numerous fibers in the transplanted 

 limbs after metamorphosis, when its functional activity comes into 

 consideration, only those which are connected with fibers in the 

 host get myelin sheaths; the superfluous fibrillae supposedly dis- 

 integrate. It would require study of a large number of instances 

 to prove that this change in the numerical relation between the 

 intrinsic and extrinsic nerve fibers of the limb during the course 

 of development is of general occurrence; yet the establishment of 

 this fact would give us only one of the necessary premises requisite 

 to put Braus' conclusion upon a logical basis. Braus does not 

 mention the exact number of cases studied, but actual figures are 

 given in only a smgle instance. Now the relation of the size of 

 the nerve trunks within the limb to that of the connecting nerves 

 of the host, is very variable, as my own cases show, and hence 

 it is quite within the bounds of possibility, not to speak of proba- 



"■Curiously enough Braus calls to the support of his view the conditions found in the nerve to the 

 electric organ of Malapterurus, where, as is well known, the organ of each side is innervated by a single 

 large cell. Since the single fiber derived from this cell ultimately breaks up into several million twigs, 

 one would naturally suppose that this would show pretty conclusively that the fibrils must branch. As 

 a matter of fact it does, but Braus in maintaining the contrary is misled by the fact that the main nerve 

 is described as of very large caliber. The actual figures given by Fritsch show at once the untenability 

 of Braus' position. While the nerve is as a matter of fact enormous, having a diameter of i, i mm., 

 its thickness is accounted for by its sheaths. The axis cylinder is but 8 /i in diameter. There are esti- 

 mated to be 2,171,252 electric discs in the organ, each of which receives a nerve, the combined area of 

 cross section of the terminal stalks being 346,760 times the area of cross section of the original fiber. 

 Assuming each terminal twig to contain but a single fibril, though probably there are more, 

 and that there is no branching, the main axis cylinder would have to contain at least 2,171,252 fibrillae, 

 which is of course an absurdity, for in order that so many be squeezed into such small compass the 

 individual fibril, even allowing no space at all for interfibrillar substance, could not be more than 

 about .005 /.( thick, which is far below the range of visibility. 



