690 VERHOEFF AND BELL. 



received light not only of greater intensity but also of shorter wave 

 length than did the retina. 



We cannot then accept Birch-Hirschfeld's findings because we were 

 unable to obtain retinal changes, although we used light intensities 

 and exposures sufficient to injure the epithelium of the lens capsule, 

 the stroma cells and endothelium of the cornea (which he did not). 

 Judging by the relatively slight histological changes found in the cor- 

 nea by Birch-Hirschfeld, the intensity on the cornea of the light used 

 by us must have been over fifty times as great as that used by him, 

 while some of our exposures were nine times as long as his maximum 

 exposure (10 minutes) to the iron arc. In the case of the aphakic eye, 

 we obtained no ganglion cell changes in 48 hours although the light in- 

 tensity was so great that the pigment epithelium showed heat changes 

 in spite of an interposed water cell. In Birch-Hirschfeld's experiments 

 the pigment epithelium was uninjured although a water cell was not 

 used. Finally, we cannot accept Birch-Hirschfeld's findings because 

 our experiments on monkeys and on a human patient prove conclu- 

 sively that the function of the ganglion cells is not injured by light 

 of the same wave lengths and vastly greater intensity than that reach- 

 ing the retina in Birch-Hirschfeld's experiments. 



In connection with Birch-Hirschfeld's findings the following observa- 

 tions relating to the ganglion cells of normal rabbit's eyes may be 

 of significance. In the first place, within the same retina there is 

 great variation in the amount of chromatin substance in the individual 

 ganglion cells; two cells side by side may show a great difference in 

 this respect.* The sharpness with which the Nissl bodies stain in 

 thionin varies considerably with slight variations in the staining pro- 

 cedure, particularly as regards the length of time the sections have 

 been immersed in the thionin solution and the degree of dift'erentia- 

 tion in alcohol. The same statement applies also to the intensity 

 with which the nuclear layers stain. While the ganglion cells of a 

 normal retina probably never contain actual vacuoles, the arrange- 

 ment of the chromatin particles is not infrequently such that they 

 enclose spaces which bear considerable resemblance to vacuoles. 

 Occasionally a ganglion cell may contain an apparently degenerated 

 nucleus, and occasionally also a more or less disintegrated ganglion 

 cell is seen. Possibly the injury to the latter is produced by the 

 microtome knife. 



* Nissl bodies cannot be seen in fresh ganglion cells so that it is possible 

 that they are formed after death. The term chromatolysis may therefore be 

 misleading inasmuch as it means solution of substances during Ufe which may 

 have never actually existed. 



