Hardesty, spinal Nctves of the Frog. 99 



These descriptions accord fairly well with the results of 

 searches made here for growing nerve fibers, one of which is 

 represented in Plate VII, figs, i to 6. 



It is concluded therefore, that the variations found to occur 

 in the number of fibers at different levels of the dorsal and ven- 

 tral roots and in the nerve trunk as recorded in Tables I and II 

 are but the natural result of the growth of the nerve fibers. 



X. Methods and Technique. 



If a detailed account were given of the difficulties experi- 

 enced before obtaining satisfactory preparations, this division of 

 the paper would be much more lengthy than it is intended to 

 make it. 



The first and prime object was not only to obtain prepara- 

 tions in which medullated nerve fibers were so sharply differ- 

 entiated that each one stained could be readily distinguished as 

 such, but also to obtain preparations in which it could be satis- 

 factorily asserted that all the medullated fibers were distin- 

 guishable. 



Little can be said concerning the effect that the general 

 nutritive condition of the animal, the season of the year etc., 

 may have upon the staining properties of its medullated fibers. 

 It is reasonable to suppose that pathological or even certain 

 natural conditions may influence to some extent at least, the 

 stain reactions of nerve fibers as well as those of other tissues. 

 Gaule ('89) recognized season as having an influence and recom- 

 mended Rana ieniporaria in May and Rana esculenta in June for 

 the clearness with which their nerve fibers might be stained by 

 the Weigert method. Little more can be said here however, 

 than that the best results were obtained with freshly caught spec- 

 imens, and that while the experiments for a satisfactory stain- 

 ing method extended through several seasons, both the speci- 

 mens from which the results recorded in this paper were ob- 

 tained were killed in October. 



For bringing out medullated nerve fibers, treatment with 

 osmic acid was of course, the first that suggested itself. Osmic 

 acid however was found to possess several defects. These de- 



