174 



/SOLA TION OF ELEMENTS 



\CH. VII 



and also of the endymal cells of the brain. It is satisfactory for isolating the 

 nerve cells of the brain. For the epithelium of the trachea, intestines, etc. , the 

 action is sufficient in two hours ; good preparations may also be obtained after 

 two days or more. The action on nerve tissue of the brain and myel or spinal 

 cord is about as rapid. For the stratified epithelia, like those of the skin, mouth, 

 etc. , it may require two or three days for the most satisfactory preparations. 



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FIG. 143 A. FIG. 143 B. FIG. 144. 



FIG. 143. Preparation Vials for Histology and Embryology. This repre- 

 sents the two vials, natural size, that have been found most useful. They are kept 

 in blocks with holes of the proper size. 



FIG. 144. Block with holes for containing shell vials. 



$261. Example of Isolation. Place a piece of the trachea of a very recently 

 killed animal, or the roof of a frog's mouth, in the formaldehyde dissociator. 

 After two hours or more, up to two or three days, excellent preparations of ciliated 

 cells may be obtained by scraping the trachea or roof of the mouth and mounting 

 the scrapings on a slide. If one proceeds after two hours, probably most of the 

 cells will cling together, and in the various clumps will appear cells on end show- 

 ing the cilia or the bases of the cells, and other clumps will show the cells in pro- 

 file. By tapping the cover gently with a needle holder or other light object the 

 cells will be more separated from one another, and many fully isolated cells will 

 be seen. 



\ 262. Staining the Cells. Almost any stain may be used for the formalin 

 dissociated cells. For example, one may use eosin. This may be drawn under 

 the cover of the already mounted preparation (Fig. 140), or a new preparation may 

 be made and the scrapings mixed with a drop of the eosin before putting on the 

 cover-glass. It is an advantage to study unstained preparations, otherwise one 

 may obtain the erroneous opinion that the structure cannot be seen unless it is 



