558 Stewart Paton 



wliich ejeet suffieient plasma not only to form, l)ut tu 8U})i)ly material 

 in larg-e euouj^h quantity to permit of the growtli of tliis ijortion of 

 the matrix. A third example of the extreme difficulty of detiniug 

 the cell boimdaries is observed in connection with the development 

 of the lateral line where neurofibrils apjiear at a very early date 

 and where the bonds between the ganglion and rudimentary sense 

 Organs are so complex and numerous that there are countless paths 

 which the fibrils may follow as soon as they once begin to be laid 

 down. This whole question, connected with the origin and growth 

 of these bridges, is so involved that certain phases of it deserve far 

 more attention than they have yet received. 



In passing a word of caution may be iutroduced in regard to 

 the possibility which exists of mistaking these bridges or Strands 

 for the processes of neuroblasts. If sections are stained by methods 

 which are incapable of differentiating the fibrils from the surround- 

 ing protoplasm, then it is quite impossible to say with any degree 

 of accuracy whether the process of a given cell is or is not a true 

 nerve. In the very interesting report of Harrison upon his ex- 

 periments on the development of the peripheral nerves, he says that 

 in oue instance, after transplantation of the ganglionic crest with 

 the cord, sheathless nerve tibres ran freely through the peritoneal 

 cavity. As all true nerves are now known to contain neurofibrils 

 it seems to me inadvisable to refer to any long process as a nerve, 

 until by the use of a diflferential stain one has determined whether 

 the so-called nerve is anything more than the undifferentiated proto- 

 plasm thrown out from a cell. I am very far, however, from deuy- 

 ing that a nerve cell may not under certain circumstances throw 

 out a process of very cousiderable length, and in fact there seems 

 to me to be evidence that such a condition does exist in the place 

 that corresponds to what Held calls the primary nuclear free Stretch 

 of the nerve. The greatest caution should be observed in assuming 

 that mere length of process, without positive knowledge regard- 

 ing the nature of the structures contained in it, is in any sense to 

 be considered a criterion as to whether a cellular Prolongation is 

 or is not to be called a nerve. Even admitting that there is some 

 justification from a physiological standpoint in referring to an un- 

 differentiated tract of protoplasm as a nerve, it will be seen that 

 the term if used in this broad senso would give rise to endless 

 confusion, and it would at once become necessary to define its ap- 

 plication in each individuai case. 



