332 



ISOLATION OF TISSUE ELEMENTS 



[CH. X 



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gently with a needle holder or other light object the cells will separate 

 from one another, and many fully isolated cells will be seen. 



516. 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 pre- 

 serves delicate structures like the cilia of ordi- 

 nary 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, intestines, etc., the action is suffi- 

 cient 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. 



517. 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. 193), 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 prepara- 

 tions, otherwise one might obtain the erroneous 

 opinion that the structure cannot be seen unless 



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. 



518. 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. 193. 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 



FIG. 198. BLOCK WITH 

 HOLES FOR SHELL- 

 VIALS. 



The blocks are about 

 33 mm. thick and the 

 holes are bored clear 

 through, then a board 

 about 5 mm. thick is 

 nailed on the bottom. 



