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 w^all, 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 



