xxxvi Journal of Comparative Neurology. 



with Kultschitzky's lithium and ferricyanide of potassium. The result is splen- 

 did differentiation both centrally and peripherally. The nerve fibers are a very 

 intense deep blue and the ground clears well. The stain is a true sheath stain 

 very much like that of No. 43. Cross sections show that in the case of the 

 largest fibers the periphery of the fiber is most deeply stained and that the axis 

 cylinder is decolorized to a clear yellow, while the intervening medullary sub- 

 stance is very faintly tinged with blue. Smaller fibers show the same sharp 

 contour, but the whole of the myelin sheath is stained, though not so deeply as 

 to wholly obscure the axis cylinder. These are, I think, the most beautiful 

 preparations which I have secured, and, though I have not thus far used the 

 method extensively, it will prove without doubt very useful for peripheral 

 nerves. 



50 F. Flemming's fluid 11 days, sections mordanted warm for 4^ hours 

 in Wolter's vanadium chloride and aluminum acetate, stained in acid haematox- 

 ylin and decolorized by the method of Weigert. This gives very good prepar- 

 ations, about like No. 46, both as to the general low power effect and as to the 

 histological appearance of the fibers under high magnification. 



52 M. Flemming's fluid 11 days, sections mordanted in half-saturated cop- 

 per acetate 3 hours, stained in Weigert's hsematoxylin 4 hours and decolorized 

 by the method of v. Plessen and Rabinovicz. The result is poor differentiation. 

 The tissues clear well, but the peripheral nerves clear as soon as the muscles. 



53 M. Specimens stained as in the last case and decolorized by Weigert's 

 method yielded preparations which on the whole I have found most satisfactory 

 for the purposes of the present research. The nerves are well differentiated 

 both centrally and peripherally. The ground is not so transparent as in some of 

 the other cases, being a light but slightly clouded brown. Nevertheless it clears 

 well except sometimes near the outer surface where there is usually some osmic 

 blackening. Fat is, of course, a deep black, so also are the dermal bones, while 

 the cartilage, calcified cartilage, muscles, connective, nerve cells, etc., are of 

 the uniform brown color. The failure of the ground to clear so as to become 

 quite transparent is not a disadvantage, but quite the contrary, as it obviates 

 the necessity of counter-staining, while the medullated nerves are stained so 

 intense a blue that they can easily be followed among the other tissues, in favor- 

 able preparations even to single nerve fibers. The finest nerve fibers are not, I 

 think, so brilliantly stained as by some of the other methods (e. g. Nos. 46 and 

 50) so that those methods have some points of superiority over this one. 



The same method applied to specimens of Fundulus about as large as the 

 last resulted in very poor sections. I have no doubt that further experiments 

 upon the times and strengths of the various solutions would much improve 

 these latter preparations; yet the Fundulus tissues are apparently more refrac- 

 tory than those of Menidia and I doubt if they would under any circumstances 

 yield so good results. Small specimens of the little fresh water sun fish, 

 Lepomis cyanellus, when stained by this method, give a still different color ef- 

 fect. The ground is a deep but brilliant bronze color which, though darker 

 than the ground in Menidia, yet contrasts equally well with the blue fibers. 



The general low-power effect is that of an ordinary Weigert preparation, 

 but under a higher magnification the appearance is quite different, especially 

 when the fibers are examined in cross section. The periphery of the fiber only 



