THE NERVE CELL 



IBS 



of the cytoplasm. Some are fatty in nature and others appear to be 



coagulated lymph or blood that was in the cell at the time, particularly 



in the channels 



that are described 



below. 



Many nerve 



cells are among 



those animal cells 



that approach the 



limit of size that a 



cell can attain and 



still have surface 



enough to perform 



its nutritive and 



excretory ex- 

 changes. A few 



go above that size ^^ ' ? " '- r ';: : .^y^ >^\| 



and in conse- ^^^ v ^^^=^ ' -f^" ff r - 



quence are obliged 



to develop in their 



cytoplasm a set of 



channels that will 



serve to increase this power of exchange. Among these are many 



nerve cells that possess lymph channels or spaces of various degrees 



of size and efficiency. These lymph channels can be seen, weakly de- 

 veloped, in the sympathetic 

 ganglion cells of the musk- 

 rat (see Fig. 158), and more 

 strongly shown in the larger 

 nerve cells of the squid (Fig. 

 156), in which latter form 

 they also are occupied, in 

 part, by the connective-tissue 

 fibrils that penetrate the cell 

 substance. More exceptional 

 is the case of the giant 

 dorsal nerve cells of the pe- 

 diculate fishes, in which the 

 capillaries themselves, with 

 their coat of connective- 

 tissue cells, enter the cytoplasm of the cell and supply it with a medium 



of exchange (Fig. 161). 



It has been noted above that connective-tissue fibrils enter the neuro- 



conn.i. 



FIG. 162. Large nerve cells from sub-oesophageal ganglion of Helix, 

 conn.t., connective-tissue elements invading cytoplasm; gr., gran- 

 ules in the cell channels. Xjoo. (From a preparation by McCLURE.) 



FlG. 163. Spinal ganglion nerve cell from electro- 

 cuted man. pg., pigment mass lying in cytoplasm 

 next to implantation cone. X 1000. 



