348 THE NERVOUS CYTOLOGY OF PERIPLANETA ORIENTALIS. 



X. CELLS FIXED IN VAPOR OF FORMALIN. 



i. Technique. — Fresh ganglia were exposed to the vapor of concentrated forma- 

 lin for one hour and twenty minutes, then passed through the alcohols, embedded, 

 cut, stained, and mounted as described for picroformalin. 



2. Observations. — The results of this method were eminently satisfactory. The 

 cell-spaces were evenly filled by the cells. The nuclear membrane was even, distinct, 

 and entire. The nucleus presented a homogeneous appearance, took a pretty even 

 stain, and contained deeply stained nucleoli. It presented no evidence of reticular 

 structure. In some cases its substance had shrunk a little, leaving a small clear space 

 just inside the nuclear membrane. The cell-body was occupied throughout by an 

 anastomosing network of fine fibrils staining clearly, but not intensely. Under strong 

 magnification small granules and masses were seen at the nodal points and along the 

 strands. The rest of the cell-body (i.e., the interstices of the network) was clear. 

 While the different cells varied both in the thickness of the fibrils and the size of the 

 meshes (just as the fresh specimens did), the most striking difference in their appear- 

 ance was caused by the varying quantities of the deeply staining granules and masses. 

 Thus some of the cells were pale, and composed of a fine granulated reticulum, while 

 others took a strong stain and presented a mass of granules, disposed in areolar fashion, 

 somewhat as in the granular zone of picroformalin preparations. In none of the 

 cells was there any peripheral laceration of the reticulum or any tendency to the 

 formation of two zones, both the reticulum and the deposit upon it being evenly 

 distributed (PL XXVII, Figs. 30-33). 



XL CELLS FIXED IN GRADED FORMALIN SOLUTION. 



i. Technique. — The ganglia were immersed successively in 1%, 2%, 3%, and 4% 

 formalin solutions, remaining in each solution one-half hour. The subsequent 

 treatment was like that in the preceding method. 



2. Observations. — The whole tissue gave evidence of considerable swelling, the 

 interfibrillar spaces were considerably enlarged, and the cell-spaces, of course, par- 

 took of this change. The nuclei exhibited a reticulum with amorphous matter and 

 nodal enlargements upon it (Fig. 34). The nuclear membrane was even and usually 

 spherical in outline, as though distended. The outlines of the cell-body were irregular 

 on account of the adhesion of some parts of its periphery to the wall of the cell-space, 

 thus causing long processes in various directions. The reticulum was very clear and 



