COMMISSURAL NEURONES 397 
3. A third lot of frogs was received on September 21, and fifty- 
two were doubly operated, having their spinal cords destroyed and 
their sympathetic trunks divided between the seventh and 
eighth autonomic ganglia. Thirty-seven survived the operation 
and were later stained by one or the other of the two methods 
employed. In all but three of the specimens operated in this 
manner both sympathetic trunks were severed. The three 
specimens referred to (28, 29, 31) will be described separately. 
Specimens 1 to 10 of this lot were allowed twenty-eight to 
twenty-nine days for degeneration and were then injected with 
methylene blue. Specimens 30 to 36 were operated at a later 
date, but were allowed about the same length of time (twenty- 
seven days) for degeneration. Specimens 11 to 13 were allowed 
thirty-six days, and specimens 14 to 29, thirty-one days for degen- 
eration. Excepting specimens 28, 29, and 37, the posterior 
ganglia of all but the first gave uniform results. 
In the posterior ganglia (all mounted on one slide) of the first 
specimen, two or three spirals were found, and a few darkly 
stained, evidently preganglionic fibers, but no pericellular baskets. 
In the posterior ganglia of all the rest there was a striking 
and complete dropping out of all spirals and pericellular networks. 
The anterior ganglia (1.e., the ganglia of the anterior sections 
of the sympathetic trunks) of the same specimens exhibited con- 
siderable variation in the number of spirals and pericellular net- 
works. In some cases they gave practically normal histological 
pictures, in others, only a few spirals and networks could be 
found. This variation did not appear to be due to irregularity 
of staining and could probably be accounted for by the fact that 
the level to which the spinal cord was destroyed varied consider- 
ably in different specimens, probably enough to vary the number 
of normal white rami joining each sympathetic trunk by one or 
two. 
Specimen 27 gave results the description and illustration of 
which will suffice for all the rest (except 28, 29, 37). 
This specimen was operated on October 5, and after an elapse 
of thirty-one days was injected with methylene blue. It was found 
that the spinal cord had been destroyed to the fourth vertebra, 
