256 E. VICTOR SMITH 



ammonium hydroxide. The material thus fixed was stained by 

 the silver reduction method of Ramon y Cajal (see ''Ergebnisse 

 der Anatomie und Entwickelungsgeschichte," vol. 16, page 178). 

 Some material that did not stain well by the silver reduction 

 method was counterstained with Delafield's hematoxylin which 

 colored the nerve fibers and capsular nuclei intensely and the 

 Schwann's sheath very delicately. 



Material fixed in formalin gave good results as regards the cap- 

 sule, capsular nuclei and the nuclei of the sensory cells, while 

 material fixed in ammoniacal alcohol gave good pictures of cell 

 outline, cell structure, and nerve processes. 



If preserved for any length of time in alcohol the material 

 depreciated. The best results were obtained from material that 

 was carried through the fixing and staining processes without 

 delay. 



In the dorsal region, the sympathetic and sensory ganglia 

 are so united that it is difficult to separate them, accordingly they 

 were treated and sectioned together. In almost every instance 

 the sympathetic ganglia took the silver stain readily, but cells of 

 the sensory ganglia were more refractory. This made it necessary 

 to employ a large number of preparations. The ganglia of old 

 birds stained more readily than those of the younger birds. 



A. SENSORY GANGLIA OF THE CHICK 



There are several structural features that are common to the 

 nerve cells of the different ganglia of the chick and other birds — 

 as individual variation in shape, and in position of nuclei, the 

 surrounding capsule, etc. — that need not be separately described 

 for each ganglion. The predominating type of unipolar cell, 

 with unequal branches of the main process, is the result of modifi- 

 cation. In embryonic stages the nerve-cells start as bipolar 

 (usually oppositi-polar) cells and change into the unipolar con- 

 dition. In the chick of eleven to fourteen days incubation the 

 process of change is well under way and numerous gradations 

 are to be seen. In adult birds most of the ganglion cells are in 

 the unipolar stage but there remains about 2 per cent of bipolar 

 cells in various stages of transition. 



