350 THE NERVOUS CYTOLOGY OF PERIPLANETA ORIENTALIS. 



XIII. POST-MORTEM CHANGES IN THE CELLS. 



i. Technique. — A roach was decapitated, opened along its back, and placed in a 

 small bottle of distilled water containing a piece of blue litmus paper. Seventeen 

 hours later, the litmus paper having become red, the ganglia were removed. One 

 was fixed in graded formalin solutions (1%, 2%, 3%, 4%), one in picroformalin, and 

 one was teased and fixed with formalin vapor. The first two were then sectioned 

 and all were treated according to the usual methods already described. In 

 each of the following experiments the same three methods were used. The 

 first afforded thin sections of cells in very nearly the fresh state. The third 

 gave a view of the whole cell in a similar condition. The second yielded 

 sections showing the action of a reagent tending to cause perinuclear concentration 

 of the chromophilic substance together with peripheral laceration and distortion of 

 the reticulum. The superiority of formalin vapor over the graded formalin method 

 for fixing material for sectioning was not appreciated at the time these experiments 

 were begun or it would have been used instead. 



2. Observations. — The cells fixed in graded formalin (PI. XXVII, Figs. 38, 39) 

 showed some loss of definition of the cytoreticulum, and upon it a very even and gran- 

 ular-looking deposit of the blue staining substance. The different cells did not vary 

 as much in the amount of this substance as in normal preparations. The picrofor- 

 malin preparation (PL XXVIII, Figs. 40, 41) gave a result in no way different from that 

 just described, there being no perinuclear concentration and no laceration of the 

 peripheral portion of the reticulum. No previous picroformalin preparation had 

 exhibited any such appearance. The teased specimens fixed in formalin vapor showed 

 the same features. In other words, the cells had already been fixed and the deeply 

 staining blue substance had been deposited upon the reticulum before the fixing 

 reagents were ever applied to them. 



One slide of a series of normal material, fixed in graded f ormalin, was next taken 

 and its cover removed. It was then immersed in a 0.4% solution of sodic hydrate 

 for four hours, after which it was restained and mounted. The general pallor of the 

 cells was striking. The cytoreticulum had lost some of its clear definition, and the 

 sparse and irregular deposit of blue staining substance upon it had lost much of its 

 affinity for the dye. In many cells there was a blotch of blue stain suggesting a large 

 colloid coagulum (PL XXVIII, Figs. 42-45). The alkali possessed an evident solvent 

 action over the blue staining substance. Thus this substance reacts as Held found 

 the chromophilic substance in vertebrate nerve-cells to do. 



