18 



stratified epithelia, like those of the skin, mouth, etc., it may require 

 1 to 3 days for the most satisfactory preparations. After the tissue 

 has remained in the dissociator a sufficient time, scrape the epithelial 

 surface gently with a scalpel and place the scrapings on a slide in a 

 drop of dissociator; cover and examine. If one proceeds after two 

 hours or so, probably most of the cells will cling together, and in 

 the various clumps will appear cells on end showing the tops or 

 bases, and other clumps will show the cells in profile. 



Tap the cover gently with a needle-holder or other light object 

 in order to separate the cells from each other more completely. 

 Many fully isolated cells as well as cells in groups will be seen. Ex- 

 amine carefully. 



40. Staining. Scrape gently the epithelial surface in a fresh 

 spot and place the scrapings on the slide in a drop of eosin ( 114) 

 or congo red ( 118). Mix well so that the stain can penetrate. If 

 for temporary examination, cover immediately and examine as be- 

 fore. For methods of making permanent preparations of dissociated 

 cells and mounting in glycerin, see 151. 



41. Formaldehyde Dissociator. Formula: 40% formaldehyde 

 (formalin), 2 c. c.; physiological salt solution, 1,000 c. c. (i. e., 

 .08% sol. of formaldehyde in normal salt solution). This is a good 

 general dissociator and as such may be employed instead of Miiller's 

 fluid dissociator. It is especially serviceable in the isolation of the 

 nerve cells of the brain and spinal cord [13], and for its use with 

 that material, see 151. It is however excellent for the dissocia- 

 tion of epithelia. 



42. Osmic acid. A 1-10% solution of osmic acid is a valua- 

 ble dissociator, especially serviceable in the isolation of nerve-fibers, 

 my clinic and amyelinic, and when fat is present, since fat and the 

 myelin of myelinic nerve-fibers are blackened by it. Twelve to twen- 

 ty-four hours generally affords sufficient time for it to act. ( 193, 



43. Sulphuric Acid. This is used in the concentrated form 

 as a dissociator of the epithelial cells of hair, horn, and nail. If 

 heated, a few minutes suffice; employed cold, a day or two may be 

 required. 



44. Nitric acid dissociator. [8] Formula: Strong nitric 

 acid, 20 c. c.; water, 80 c. c. See 189a. This fluid is employed in 

 the isolation of muscle fibers, both striated and plain. 



