xxxviii Journal of Comparative Neurology. 



for the separation and tracing of coarse and fine fibered components. 

 The tissue, however, is of poor consistency for serial sectioning and 

 furthermore cannot be stained by any of the Weigert processes which 

 I have tried. 



Flemming's fluid is the most generally satisfactory fixer. The fix- 

 ation is nearly as good as that of Hermann's fluid, the decalcifying 

 power is considerable, the tissue is in good histological condition for 

 serial sectioning and permits a variety of excellent Weigert stains. 

 The Haidenhain iron-haematoxylin (No. 40) and Mallory's haematoxylin 

 after copper mordanting (No. 41) both give very beautiful sections of 

 the central nervous system. Vassale's method (No. 43) promises well 

 and with slight modification gives results which are nearly as good as 

 those of the longer processes. Several of the more usual methods, 

 after slight modification, give very excellent results centrally and peri- 

 pherally, some using an acid stain (Nos. 46, 50) and some the akaline 

 stain (Nos. 53, 54). The most successful preparations were all mor- 

 danted in copper except No. 50 (vanadium and aluminum). The 

 osmium in the fixing fluid is not of itself a sufficient mordant either 

 for the acid or the alkaline dye. The stain in all of these Flemming- 

 hardened specimens is quite unlike the usual Weigert effect, since the 

 periphery of the myelin only is deeply stained (and this applies both 

 in the brain and in the nerves outside), while the deeper parts of the 

 medullary sheath are stained more feebly or not at all and the axis cyl- 

 inder usually decolorizes to a yellow or brown like the general ground 

 tissues.^ 



Vn. — FIXATION WITH FORMALIN. 



Most of the experiments described under this head w^ere suggested, 

 as intimated above, by Bolton's results with human tissue. His meth- 

 ods were repeated in several cases as exactly as possible, but with quite 

 dissimilar results, as we shall see. I am indebted to my pupil, Mr. L. 

 I. Thayer, for assistance in carrying out this series of experiments. 



59 M. The brain was hardened in 20 per cent, formalin for six months, 

 washed in water, embedded and sectioned in paraffin, the sections mordanted 



' It should be added that here, as usually with osmic-hardened material, the 

 specimens should be cut soon after preservation, as a prolonged stay in alcohol 

 is very detrimental to the staining powers. In attempting to repeat the method 

 described in No. 53 upon specimens which had lain more than a year in alcohol 

 I found it impossible to get even a tolerably good stain. Possibly preservation 

 in cedar oil would remove this difficulty, though I have not as yet tried it. The 

 safest way to preserve for long periods is unquestionably to embed and leave iu 

 the block. 



