576 Stewart Paton 



of the axon apparently euds near the cell and only the fibiils are 

 continued beyond this point. 



7) One of the chief histological characteristies of the fuUy 

 diflferentiated nerve is that it coutains neurotìbrils, aud every bit of 

 evidence so far accumulated i)0ÌDts to the appearance of these 

 structures as marking the period of greatest physiologieal activity 

 in any given nerve. 



In view of these facts it is an assumption to designate the 

 process of any cell as a nerve, unless it can be shown to contain 

 neurofibrils. 



Section 3. 



Fixation and Staining of Material. 



The method of fixing and staining the material finally adopted 

 by me as g'iving the best results in embryos is a modification of the 

 technique recommended by Bielschowsky. Several of the suggestions 

 made by Wolff (Biol. Centralbl. 25. Bd. 1905) vrere also acted 

 upon. The chief differences between the method as originally 

 described by Bielschowsky and as I have used it are the follo wing: 

 1) the Substitution of 0,75 or \% solution of Silver nitrate, in- 

 stead of the 2^ Solutions generally employed; 2) the combination 

 of formol with hydrochinon as a developer; 3) staining in a neu- 

 tral gold bath of Vio^ö instead of \%^ and 4) following the 

 Suggestion of R. Gast the subsequent staining of the cytoplasm 

 with eosin or other dyes. 



1) The material is fixed in a 4^ solution of formol neutralized 

 by the following method. To the ordinary 40^ commercial formol 

 sufficient carbonate of magnesia was added to give the fluid a 

 neutral or very faintly alkaliue reaetion when tested with litmus. 

 Generally after the fluid has been allowed to stand for several 

 hours and the magnesium carbonate has fallen to the bottom of the 

 bottle it will be found necessary to add more of this reagent. 

 After the reaetion of the Formol has become permanently and de- 

 finitely neutral or very slightly alkaline the supernatant fluid is 

 carefully poured off and filtered. One part of this stock solution Ì3 

 theu diluted with 10 i)arts of tap-water as occasion requires. 

 Embryos may be left for any length of time in the ^% solution 

 without interfering with the subsequent staining. 



