No. 4-] AMPULLAE OF THE SELACHII. 165 



exposure. Indeed, by careful watching one can see the stain 

 creep along the nerve trunks and the fibrillae out to the finest 

 ramifications. If the stain has worked successfully the fine 

 fibrillae will stand out as sharp blue lines all over the surface of 

 the ampulla, all the rest of the tissue remaining colorless. 



Fixation of the blue is accomplished by removing the am- 

 pullae into a solution of ammonium molybdate. I have modi- 

 fied somewhat Bethe's original formula (Archiv f. mik. Anat., 

 1895, Bd. xliv, pp. 579-588) in substituting osmic acid for 

 hydrochloric, using the following solution : 



Ammonium molybdate . . . i gr. 



Distilled water . . . . 10 cc. 



Peroxide of hydrogen . . . i cc. 



Osmic acid, i f . . i drop. 



This mixture seems to fix the blue stain more perfectly than 

 any other I have tried, and has two additional advantages : 

 first, that of differentiating the medullary sheaths of the 

 nerves; secondly, that of better histological preservation of 

 the tissue. I have not found the use of ice, recommended by 

 Bethe, necessary for the preservation of the blue. 



After remaining in the fixing fluid for one to two hours the 

 ampullae are washed in water for ten minutes, then hurried 

 through the grades of alcohol, cleared in toluol and imbedded 

 in paraffin. Since these organs are so small (about i mm. in 

 diameter), twenty minutes in each fluid and an hour in paraf- 

 fin I find to be sufficient. An injection of the blue may 

 therefore be made at 10 A.M. and by 5 P.M. one may cut a 

 series of sections. The histological character of the cells after 

 such treatment is not very perfect, but the nerve fibers with 

 their branches stand out very sharply defined. 



Since alum carmine does not impair the blue it has given 

 the best results as a nuclear stain for sections. 



Many facts of nerve relations can best be determined by 

 treating the tissue in the following way. Ampullae well 

 stained with the methylene blue are fixed in ammonium picrate, 

 and frozen by the use of carbon dioxide on a freezing micro- 

 tome attachment. Freehand sections are cut with a razor 



