ti NEUROKERATIN IN’ THE MEDULLARY 
Site brs (OR THE) PERIPHERAL 
NERVES OF MAMMALS. 
By SHINKISHI HATAI. 
(From the Neurological Laboratory of the University of Chicago.) 
With Plate IV. 
At as early a date as 1876, EwaLp and KUHNE announced 
that the nervous system contains a horn-like substance which 
has a great resistance to chemical reagents and especially to 
gastric and tryptic digestive fluids. Onaccount of its similarity 
to the horny material found in other tissues, they termed the 
substance obtained from the nervous system ‘‘Neurokeratin.”’ 
JOSEPHINE CHEVALIER, in 1884, demonstrated the presence of 
the neurokeratin in the medullary sheath of the peripheral 
nerve fibers, by means of chemical analysis. Later (1890) 
CHITTENDEN again took up the problem of the neurokeratin with 
Professor KUuNEg, the first investigator of it, and not only con- 
firmed the previous statement of EwaLp and KUuHNE, but at the 
same time cleared up many obscure points. In addition to the 
chemical determination of it, they showed also that the neu- 
rokeratin network in the medullary sheath may be demonstrated 
under the microscope by treating the fiber with boiling alco- 
hol, ether and digestive fluids. By examining under the micro- 
scope the slides thus prepared KUHNE and CHITTENDEN arrived 
at the conclusion that there are two layers of the neurokeratin 
network in the medullary sheath; one closely surrounding the 
axis cylinder, the other lying immediately beneath the primi- 
tive sheath. 
Through the investigation of these writers just mentioned, 
the new field of the study was opened for the neurologist. 
There are a large number of articles concerning the neuroker- 
