CRANIAL NERVES OF SIREN LACERTINA 247 
METHODS AND TECHNIQUE 
The present paper is based upon the study of young adults of 
Siren lacertina 140 to 220 mm. in length, fixed and stained in 
vom Rath’s solution of the following composition: 
Bicrichackds satin aved SOMULONM ihe sack selectes cisie i. «ccs asic re eee 250 ce. 
Platinic chloride (dissolved in 5 ce. of water)... ............. 2.5 grams 
MTSE LCA, oR clas SP NPM) cielo RE wie 6 os, lh Laue ene 1 gram 
Glacialea cet ce aGalenertscrraice ton siey is cake a aio at tve wees slate clo ass oe Oe 5 ee 
The duration of the fixation and accompanying decalcification 
was about ten days. This was followed by washing in running 
water twenty-four hours, in 50 per cent and 70 per cent alcohol 
until the excess of picric acid was removed. The customary 
treatment with pyroligneous or pyrogallic acid was omitted, as 
the increased blackening of the general tissues thus produced has 
been found to be detrimental to the tracing of the peripheral 
nerve fibers. The material was imbedded in celloidin after 
months of infiltration, beginning with 0.5 per cent solution and 
ending with a 20 per cent solution. The sections, cut 20u in 
thickness, were counterstained on the slide in Van Giesen’s 
picro-fuchsin. Sections prepared by the celloidin method, as 
thus employed by the writer with specimens of considerable size, 
have many advantages over those prepared by the paraffin method. 
Their clearness, freedom from distortion and contraction, and 
absence of displacement of parts, more than offset their thick- 
ness (20u) and the tedium of the prolonged section cutting. When 
the treatment with pyroligneous acid is omitted in the vom Rath 
procedure the hot melted paraffin and its subsequent removal 
by xylol, and so forth, in the paraffin method bleach out to a 
considerable extent the osmic acid stain. By the celloidin method 
the stain is apparently unaffected, even when the infiltration is 
continued six months. Sections were cut in the three conven- 
tional planes. Despite the thickness of the sections the fixation 
and differentiation have been so precise that there has been 
little difficulty in tracing and distinguishing the various nerve 
components. Even the fine twigs to the individual neuromasts 
