366 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
connective-tissue cells and muscle cells was dissolved. The epidermal 
cells were vacuolated and their nuclei were undergoing chromatolysis. 
The gland cells had often lost their contents. 
Especial attention was given to the condition of the supra-oeso- 
phageal ganglia and nerve cord, because of the differences of opinion 
as to the sensitiveness of the central nervous system to radium. 
Danysz (:03) exposed the brain of the mouse to radium after tre- 
panning the skull, and he described as a result the necrosis of the 
nerve cells. Rehns (:05), upon the other hand, found little injury 
in the brain of a rabbit with skull trepanned. Bohn (:03), Scholtz 
(:04), Obersteiner (:04), and others describe an especially marked 
degeneration in the central nervous system of animals whose entire 
bodies had been exposed to radium. Birch-Hirschfeld (:05) found 
it to be the nervous elements of the rabbit’s retina which most quickly 
succumb to beta rays. The fact that the central nervous system 
readily degenerates does not, however, prove that it is especially 
sensitive, since it contains much vascular tissue and this is well known 
to be highly sensitive to radium. Observers have been divided as to. 
whether the degeneration of nervous tissue was actually a primary 
effect of the radiation, or produced by the necrosis of the vascular 
endothelium and the resulting hemorrhage. 
In the earthworm the nerve cord is associated with much less vas- 
cular tissue than is the spinal cord in the mammal. This makes it 
possible to ascertain whether the nervous tissue is of itself especially 
sensitive to radium. A careful examination showed that the ganglia 
and nerve cord are no more sensitive than the body wall, and were 
necrotic only when it also was affected. The ganglion cells were, - 
naturally, the first elements of the nerve cord to show injury. Later 
the fibre tract lost its structure and the nuclei of the neuroglia cells 
were broken down. The Nissl flakes did not give evidence of any 
injury to the nerve cord or ganglia in cases where the body wall 
remained normal. Furthermore, pigment deposits were found in the 
body wall of worms whose nerve cord was in good condition. Inas- 
much as the pigment is probably a product of decomposition of the 
blood, this is an indication that the vascular system, as in mammals, 
is very sensitive to beta radiations. 
The Nerve Cord of the Crayfish Cambarus affinis. 
In the crayfish (Cambarus), as well as in Allolobophora, the central 
nervous system is much freer from vascular tissue than in mammals, 
and furnishes, therefore, a favorable object for determining whether 
