21 

 tion, fresh from the open sea, if possible. But even with 

 this precautionary recognition of physiolofsical conditions, so 

 far as they could be readily determined, there apparently yet 

 remained some unknown factor which caused a negative result 

 in some instance where it was least expected. 



S, Iron HaematoxiJ I in . 



This reagent was imagined^ by Heidenhain ('9?) for refined P 

 cytological work, but it truly has a place in neurological in- 

 vestigation. It is a most excellent stain for defining the 

 internal structure of the nerve-cell, and also for the tracing 

 of nerve-fibres. F'or the latter purpose, iron haematoxylin 

 has proven itself preferable in this research to the stain of 

 Weigert, since it defines the axis-cylinder instead of the 

 myelin, permitting fibres to be followed through their rariiifi- 

 cations entirely to the terminal arborisations. 



Fixation of the tissue may be done with any good fluid. 

 Where the tracing of axones, only, is desired, 10"? formalde- 

 hyde cannot be surpassed; but where the aim is purely cytolog- 

 ical, either the chrome-oxalic mixture of Graf or the fluid of 

 Plemming will give superior results. For work on axis-cylinders, 

 celloidin sections were made 30 micra thick; and for- the minute 

 study of the nerve-cell, thin sections were cut by the paraffin 

 method. . 



The sections were brought from distilled water into the 



