76 JouRNAL OF ComPaRATIVE NEUROLOGY. 
indicated by Gotar (’94); by Ramon y Caja ('94); by FLECH- 
sic (’89); by Cox (’91); and by Srrone (’95, ’96). Every 
application practicable was also made of formaldehyde as a con- 
stituent of the reagents employed. A general critique of these 
processes has already been given by me ina former paper (’97a). 
The slices of perfectly fresh brain from the most active 
animal procurable were placed in the ‘‘rapid’”’ hardening mix- 
ture of Gotct. The pieces were always small, not over two 
millimeters in thickness for, ¢. g., a transverse section of the 
forebrain. The proportion of the hardening fluid used embraced 
one part of 1% osmic acid to four parts 3.5% potassium bi- 
chromate, and this reagent was used in liberal quantities. The 
proper duration of hardening was influenced by the temperature 
of the room and the physiological state of the animal, but an 
average length of time was three days. The greatest clearness 
of impregnation was secured with silver nitrate solution of 
0.75% strength. In the preparation of serial sections, the most 
desirable clearing agent was found in a mixture of oil bergamot, 
oil cedar-wood, and melted carbolic acid crystals, equal parts. 
After being hardened in chloroform, the celloidin blocks were 
placed in the clearing mixture, and they were kept flooded with 
the oil during cutting. The above mixture clears the block 
rapidly, it may be used repeatedly, and it has the additional 
advantage of allowing the preparations to be kept in it for some 
time without impairing the impregnation. The sections were 
cut 75 micra in thickness. 
2. The Application of Methylen-Blue. 
Methylen-blue holds so many possibilities as a neurolog- 
ical reagent that we are doubtless but crossing the threshold of 
its use to-day. Ihave applied this aniline in every way of 
which I could learn, and the most important results are set 
forth below. 
a. The Staining Method of Nissl.—Nissu’s description of 
his method (’94) called for the fixation of the tissues with alco- 
hol. This has proven an unsatisfactory part of the technique 
for my work. Better cytological preservation by far has been 
