I50 JOURNAL OF COMPARATIVE NEUROLOGY. 
atin, but it is not necessary to review them in detail. Generally 
speaking, two different opinions are held by the recent investi- 
gators; one, according to which the neurokeratin is not a pecu- 
liar substance, but an artefact produced by the reagents em- 
ployed, an albuminous substance (RANVIER) or a nucleoproteid 
(Wynn). This view is held by several histologists, for instance, 
ENGELMANN, GERLACH, KOLLIKER and LAvpowsky. The sec- 
ond view, that the neurokeratin is a peculiar substance in the 
nervous system and preexists as such, is held by most of the 
physiological chemists as well as by a number of histologists ; 
for instance, Lrypic, PALUDINO, JOSEPH, SCHIEFFERDECKER, 
KapLan and others. 
In recent years the use of WEIGERT’s and HEIDENHAIN’S 
haematoxylin has given many opportunities to study the struc- 
ture of the neurokeratin, and as a consequence, a large number 
of reports have already been made. Most of the recent inves- 
tigators are inclined to believe in the preexistence of the neu- 
rokeratin in the medullary sheath, on both chemical and histo- 
logical grounds, and moreover the complexity of the neuroker- 
atin increases as the technique improves. 
Before discussing the literature further, I shall give an ac- 
count of my own results. 
For this investigation, the nerve fibers were preserved in 
10% formalin and cut into sections 1oyv thick after the usual 
paraffine technique. The sections were stained with the ‘‘blue 
solution’”’’ and decolorized sufficiently with diluted NHsOH. 
In some cases the blue solution was used without subsequent 
decolorization. 
The preparations thus treated show the double layers of 
the neurokeratin network in the medullary sheath, one layer 
closely surrounding the axis cylinder, while the other lies just 
beneath the primitive sheath as was stated by EwaLp and 
KUxNE and others. Such an arrangement of the neurokeratin 
1 Preparation of the ‘‘blue solution’’ and its application to the microscopical 
sections is given in my other paper,—‘‘ On the Nature of the Pericellular Net- 
work.”? Journ. Comp. Neurol., Vol. XIII, No. 2, p. 141. 
