124 ALAN C. SUTTON 



now be put in fresh absolute alcohol in a warm room. It is 

 hurried on through xylol into paraffin. This is the only per- 

 manent fixation of the methylene blue stain. 



The other method is to place the tissue in filtered saturated 

 ammonium picrate overnight; clear it in equal parts of this 

 picrate solution and glycerine; mount in pure glycerine. This 

 method is not permanent but the endings remain distinct for 

 about a month. AAHiile I studied some of my material by the 

 ammonium molybdate fixation (as Wilson gives this as the most 

 reliable method) I found that it had few advantages over the 

 armnonium picrate preparations, except that it is permanent, 

 nicer to work with, and the thin sections give a better picture 

 of the individual muscle fibers — which can be counterstained. 

 The advantages of the glycerine mounts are these: one can ex- 

 amine much larger pieces of tissues — even an entire muscle of the 

 smaller embryos— under a single cover-slip. The nerve plexus, 

 the individual nerves and their relation to the spindles can be 

 studied without having to follow them through several sections. 

 Above all, the spindles can be teased out and examined sepa- 

 rately. With this fixative the nerves stain violet and the muscle 

 yellow. The muscle striations and nuclei can be seen without 

 difficulty after one becomes accustomed to working with the 

 material. 



It was my habit to make sketches of and study the fresh as 

 well as the fixed material. Of course it was impossible to study 

 a fresh specimen and then fix it, as they fade so rapidly, and for 

 good fixation it is necessary to place the tissue in the fixing- 

 fluids before the endings show up very sharply, othei'wise many 

 details are lost, as the fixatives have the tendency to overoxidize 

 and dissolve out some of the stain. 



The methylene blue is not absolutely specific for nerve tissues 

 and quite a httle practice was necessary before being absolutely 

 sure of my ability to say what was nerve and what was not. 

 One of the best clues in the identification of a nerve is the densely 

 staining nodules that appear at short intervals along the non- 

 medullated nerve. The medullated nerves are easily recognized 

 by the deeply staining nodes of Ranvier. There is no difficulty, 



