COMMISSURAL NEURONES 387 
of cerebrospinal origin and whether or not endings of any other - 
type are present. 
My thanks are due to Prof. S. Walter Ranson for many cour- 
tesies extended during the course of the experiments. 
Il. MATERIAL AND METHOD 
Material for the observations reported below consisted of three 
separate lots of frogs (Rana pipiens), as follows: 1) six dozen 
winter frogs received March 20; 2) six dozen frogs received 
June 7; and 3) six dozen summer frogs, received September 21, 
1917. The first two lots were operated only for destruction of 
the spinal cord by reaming the spinal canal with a hot, flat needle 
(Huber, Jour. Morph., vol. 16, p. 50), approximately as far 
cephalad as the second vertebra. In the frogs of the third lot 
the spinal cords were destroyed as just noted and in addition, 
in order to eliminate preganglionic fibers which might enter and 
run caudally in the sympathetic trunks, from the anterior un- 
damaged part of the spinal cord, both sympathetic trunks were 
severed between the sixth and the seventh, or the seventh and 
the eighth, sympathetic ganglia. This operation was accom- 
plished through a small lateral incision just to the side of the 
transverse process of the sacral vertebra. Through this open- 
ing both trunks were caught with the aid of a hooked needle and 
snipped with a pair of fine scissors. The incision was then 
sutured, the frog tagged, and a record made of the date of the 
operation. On dissection after injection it was found that in two 
instances only one trunk had been severed and in one instance 
both trunks were still intact. These specimens gave interesting 
results, as will be noted later. Aseptic precautions were found to 
be unnecessary. 
Two staining methods were employed, the intra vitam methyl- 
- ene blue process practically as described by Huber (Jour. Morph., 
vol. 16), and the pyridine silver method. In the former it was 
found advantageous to use 3 or 4 per cent methylene blue in 
Ringer-Locke solution. This was injected into the ventral vein 
instead of the lateral vein as described by Huber. For pyridine 
