Herrick, Nerve Components of Bony Fishes. 179 



rapid decalcifying solutions, and especially those contain- 

 ing nitric acid, are useless. So also solutions containing 

 picric acid had to be discarded, though several, such as 

 picro-forinalin and especially picro-acetic-formalin, prove 

 to be excellent fixers for general tissues; yet none of 

 them preserve the medullary sheaths properly. The 

 attempt was made to blacken the nerve sheaths with 

 osmic acid during the process of decalcification. First 

 Flemming's stronger fluid was tried. If applied for two 

 or three weeks, decalcification is complete and the tissue, 

 though very brittle, is in perfect histological condition ; 

 but the nerve fibres usually refuse to precipitate the metal 

 and appear as white cords in the generally blackened 

 tissues. 



Hermann's fluid, if applied for several weeks, decalcifies 

 and at the same time blackens the medullary sheaths more 

 or less ; but it does not leave the tissue in so favorable 

 histological condition as the Flemming. Indeed, the 

 specimens so prepared were so brittle that it proved im- 

 possible to get sufficiently continuous sections for plotting 

 and this method was finally discarded in favor of a modi- 

 fied Weigert method. Nevertheless, several series which 

 were mounted directly after fixation in Hermann's fluid, 

 without further staining, have proved of the greatest ser- 

 vice in controlling the others, as the sections, if once 

 obtained, give sharper and clearer pictures of the proper- 

 ties of the nerve sheaths than can be secured in any other 

 way. This applies especially to the peripheral courses of 

 the nerves ; the penetrating power of the fluid is so slight 

 that it is not of much value centrally. 



Upwards of a hundred modifications of the Weigert 

 method were tried, for^the most part with unsatisfactory 

 results; nevertheless some of these methods are very 



