17 



fixing and the action is very much weaker and requires from one or 

 two hours to as many days. In the weak solution the cell cement or 

 connective tissue is softened 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 fixing action is retained while the hardening 

 action is reduced on dilution. The time required for the action of 

 the dissociator varies inversely as the vehemence of the fixer and 

 the density of the tissue, 2 to 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 [15]. Those 

 chemicals that are "cytoplasmic fixers" such as potassium dichro- 

 mate, Muller's fluid, formaldehyde, osmic acid, appear to be especi- 

 ally useful in the dissociation of epithelia. 



For the isolation of muscle, alkalis or mineral acids, which soften 

 or dissolve the connective tissue are to be employed. Horn, nail and 

 hair require strong mineral acid or (usually) weak alkali. 



37. Of the many maceration fluids or dissociators the follow- 

 ing may serve most of the needs of histology: (1) Muller's fluid dis- 

 sociator; (2) formaldehyde dissociator; (3) osmic acid (1/10%); 

 (4) sulphuric acid (strong); (5) nitric acid dissociator; (6) caustic 

 potash dissociator. 



38. Muller's fluid dissociator. Formula: Muller's fluid, 1 

 part; physiological salt solution, 9 parts (i. e., potassium dichromate, 

 2.5 grams; sodium sulphate, 1 gram; sodium chlorid, 9 grams; 

 water, 1,000 c. c.)% [15]. 



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

 decreases the hardening action of Muller's fluid as is shown especially 

 on the cell-cement, hence its dissociating action. Considerable 

 latitude in time is allowed in the use of this dissociator; 12 hours 

 being often sufficient, although a stay of several days in the dis- 

 sociator usually does no harm. 



39. 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 re- 

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

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

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



