138 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



lation of tlie fluids in the central caual and the formation of artifacts 

 in the lumen of the same. Among those used were: Flemming's 

 stronger fluid, formol (5 to 10%), corrosive-acetic, Zenker's fluid, 

 potassic bichromate, bichromate-formol, picric-formt)l-acetic, Gilson's 

 fluid, Mliller's fluid, Grafs clirome-oxalic fluid, and chromic acid. In 

 material preserved in any of the fluids enumerated the fibre can be 

 plainly seen, being, however, somewhat more sharply brought out by 

 some reagents than by othei's. 



The stains which serve best for Reissner's fibre are certain of the 

 hematoxylins and certain of the anilines. Of the first class Mallory's 

 phosphomolybdic and phosphotungstic hematoxylins, and Ehrlich's 

 acetic-alum hematoxylin were the best. Iron hematoxylin brings out 

 tlie fibre well, if decolorization is not carried too far. Of the anilines, 

 methyleu blue, Congo red, and acid fuchsin were found to be the most 

 valuable. Double staining was found desirable for bringing out tlie 

 internal structure of the fibre. The most successful combination was 

 Ehrlich's hematoxylin followed by Congo red, which, by the way, is one 

 of the best of all combination stains for the central nervous system of 

 lower vertebrates. 



Vom Rath's osmic-acid methods and the Weigert methods were 

 also used effectively to diff'erentiate the sheath and finer branches of 

 lieissner's fibre. Methylen-blue impregnation has also aff'orded some 

 results. Golgi metliods, though tried in great variety, have so far 

 failed to give an impregnation of the fibre. The cells, however, which 

 give rise to the fibre of Reissner are frequently impregnated, and their 

 axons may sometimes be followed by this method, to where they emerge 

 into the ventricle. This failure of the fibre to take the Golgi impreg- 

 nation may be explained, perhaps, by the fact that the fibre is here 

 surrounded by the cerebro-spinal fluid, which contains a considerable 

 percentage of non-dializable colloid substance, thus preventing the 

 fixing fluids from reaching it readily. 



In investigating the occurrence and course of Reissner's fibre, I have 

 made and studied series of sections of the central nervous system of 

 more than three hundred individuals representing upwards of one hun- 

 dred different species, and including all the principal groups of verte- 

 brates. In addition, I have been able to draw upon a large collection 

 of preparations of the central nervous system of teleosts previously 

 prepared. All the chief groups and principal sub-groups of vertebrates 

 have been examined, and in no case where perfectly preserved material 

 has been carefully studied have I failed to find Reissner's fibre present. 



