83 



so that cells and fibers may be separated from one another, and at 

 the same time the cells are preserved. In other words, a weak fix- 

 ing attion is retained while the hardening action is reduced on dilu- 

 tion. The time required for the action of the dissociator varies in- 

 versely as the vehemence of the fixer and the density of the tissue, 

 2-3 hours to several days. In fixing and hardening, on the other 

 hand, the cell cement, like the other parts of the tissue, is made 

 firmer. It is better also to dilute the fixing agents with normal 

 salt solution than merely with water. 



§ 3. Of the many dissociators, the following may serve most 

 of the needs of histology : (1) Miiller's fluid dissociator ; (2) for- 

 maldehyde dissociator ; (3) nitric acid dissociator ;. (4) caustic pot- 

 ash dissociator ; (5) Ranvier's one-third alcohol ; (6) osmic acid 



(tV%). 



§4. Miiller's fluid dissociator. Formula: Miiller's fluid, 



I part ; normal salt solution, 9 parts {i. e., potassium dichromate, 

 2.5 grams; sodium sulphate, i gram; sodium chlorid, 6 grams; 

 water, 1,000 c.c. ). 



This is a good general dissociator for epithelia, including glands. 

 Dilution decreases the hardening action of Miiller's fluid as is 

 shown especially on the cell-cement, — hence its dissociating ac- 

 tion. Considerable latitude in time is allowed in the use of this 

 dissociator ; 12 hours being often sufficient, although a stay of sev- 

 eral days in the dissociator usually does no harm. 



§ 5. Directions for use. In the employment of this, fluid for 

 the isolation of epithelial cells, proceed as follows : 



Place the tissue covered with the epithelium which it is desired 

 to isolate in the dissociator in a shell vial or dish, where it may 

 remain from 2-3 hours to 2-3 days ; for the epithelium of the tra- 

 chea, intestines, etc., the action is sufficient in 2-3 hours, although 

 good preparations may be obtained after two days or more. For the 

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

 1-3 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 the dissociator ; cover and examine. If one proceeds after 

 two hours or so, probabl}' most of the cells will cling together, and 



