26o ISOLATION OF HISTOLOGIC ELEMENTS [CH.IX 



J 359. Example of Isolation. — Place a piece of the trachea of a very 

 ecently killed animal, or the roof of a frog's mouth, in formaldehyde dissocia- 

 tor in a shell vial or glass box. After half an hour, 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 one hour, probably most of the cells will cling together, and in the vari- 

 ious clumps will appear cells on end showing the cilia or the bases of the cells, 

 and other clumps will show the cells in profile. By tapping the cover gently 

 with a needle holder or other light object the cells will separate from one another, 

 and many fully isolated cells will be seen. 



\ 358. Isolation by Means of Formaldehyde. — Formaldehyde in normal 

 salt solution is one of the very best dissociating agents for brain tissue and all 

 the forms of epithelium. It is prepared as follows: 2 cc. of formal, (that is, a 

 40% solution of formaldehyde) are mixed with 1000 cc. of normal salt solution. 

 This acts quickly and preserves delicate structures like the cilia of ordinary 

 epithelia, 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, in- 

 testines, etc., the action is sufficient in half an hour; good preparations may 

 also be obtained any time within two days or more. The action on nerve tissue 

 of the brain and myel or spinal cord is about as rapid. 



Fig. 207-208. Slender dish and Syra- 

 cuse watch glasses for use in making 

 isolations etc. ( Cuts loaned by the 

 Whitall Talum Co.) 



\ 360. 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. 201), or a new preparation 

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

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

 one might obtain the erroneous opinion that the structure cannot be seen un- 

 less it is stained. The stain makes the structural features somewhat plainer; 

 it also accentuates some features and does not affect others so markedly. 

 Congo red is excellent for most isolated cells. 



\ 36L Permanent Preparations of Isolated Cells. — If one desires to make 

 a permanent preparation of isolated cells it may be done by placing a drop 

 of glycerin at the edge of the cover and allowing it to diffuse under the 

 cover, or the diffusion may be hurried by using a piece of blotting paper, as 

 shown in Fig. 201. One may also make a new preparation by mixing 

 thoroughly some of the isolated material with congo-glycerin. After a few 

 minutes the cover-glass may be put on and Sealed ($ 351). If one adds 

 congo-glycerin to a considerable amount of the isolated material it may be 

 kept and used at any time. 



