Smallwood and Rogers, Molluscan Nerve Cells. 51 



Our review of the work of Holmgren can give us at best but an inadequate con- 

 ception of its amount and quality. His numerous papers, while somewhat con- 

 troversial, contain a large range of observations on fixed nerve cells, both verte- 

 brate and invertebrate. His main contention seems to be centered around the 

 character of the cytoplasm. Whence come the numerous spaces in it, a ' what 

 of their character .? It seems to us necessary to include here a review of some of his 

 studies upon the nerve cells of vertebrates, since he makes this his starting point. 

 A good summary of Holmgren's ideas concerning the structure of the nerve cell 

 may be found in vol. II of Merkel and Bonnet's Ergebnisse. 



Holmgren ('01) makes the first mention of the "Saftkanalchen" in the spinal 

 nerve cells in his paper on Lophius piscatorius, where he makes the following 

 statement, "localized endocellular nets of 'Saftkanalchen' are seen especially well 

 in the rabbit." A thick network of fine tubules is to be seen in the cytoplasm 

 surrounding the nucleus, and usually near the poles of the cell. The sectioned 

 lumina of the tubules are always circular in outline and are always sharply marked 

 off. Here and there one can find how these networks of tubes are connected with 

 the pericellular tubes. In these places the walls are clearly marked. Within the 

 cells the author could see no definite walls to the canals. Most of the cells of the 

 spinal ganglia possess such networks, but they do not always seem to agree with 

 each other with respect to the breadth of the lumen or the wall of the canal. 



In the cells the author distinguishes two cytoplasmic zones, an inner canalicular 

 and an outer extra-canalicular zone. These canals are supposed to have walls — 

 at any rate something which appeared to be a wall stained red with erythrosin. In 

 addition to the observations just cited upon the rabbit, the author studied the d g, 

 cat and various birds. In these animals he found remarkably strong dilated 

 canals winding in a corkscrew manner through the ganglion cells. From the peri- 

 or extra-cellular tubes more or less numerous canals force their way into the ganglion 

 cells. Inside of the cell they often divide in the characteristic finger-form manner, 

 and they turn in manifold ways, not infrequently in spirals. By this means there 

 exist glomerulus-like collections of tubes in the cell. In the case of the birds there 

 were seen canals so strongly dilated that the protoplasm appears only as islands or 

 thread-like heaps between thetubes. These dilations ortubes are notlocalized in any 

 particular part of the cell but may be found in any part. He says that these tubes 

 must correspond to the bands which were described by Nelis, with the exception 

 that Nelis did not make any mention of bands going out of the cell. Such con- 

 nections do not exist in all cases, but are nevertheless general. Holmgren could 

 find these cells in the sympathetic and central nervous system of birds. He con- 

 sidered the canals which may be continued beyond the limits of the nerve cell as 

 lymphatic passages. 



As opposed to Studnicka, Holmgren says that the lymph canals come from 

 the anastomosis of vacuoles or alveoli, and again he states that the canals in the 

 case of Petromyzon are bounded by intensely staining walls which continued rcctly 

 outside of the nerve cell into the walls of the extracellular paths. 



If one stimulates the spinal ganglion cells by means of weak induction currents, 

 almost all parts of the whole canal are strongly widened. This agrees with the 

 statement of Nelis that the bands occur in altered cells. "The nerve cells are 

 permeated with a very rich canal system hitherto unsuspected, and only the more 

 dilated parts of these networks are the passages which I was able to see befo ." 



