10 ' Fixation (chap. 1) 



with it until immediately before use. If acetic acid is added, mitochon- 

 dria are lost, but chromosomes are shown better than when the chro- 

 mate is used alone. It usually is necessary to wash out the dichromate 

 with water in order to prevent the formation of an insoluble precipi- 

 tate of CroOs; this will form if the tissue is carried directly to alcohol. 



Trichloracetic Acid, CCl.fiOOH 



This acid never is used alone and is similar to acetic acid in action. 

 It swells tissues and has a slight decalcifying property. As was noted 

 inider acetic acid, washing should be done in alcoholic solutions. 



"Indifferent Salts" 



Baker (1958) applied this term to a group of chemicals (sodium sul- 

 fate, sodium chloride, and others) the action of which is not clearly 

 understood. Zenker's and Helly's solutions often have sodium sulfate 

 added. Sometimes sodium chloride is added to formalin or mercuric 

 chloride fixatives, particularly when marine forms are to be fixed. 



References: Baker (1945, 1958). 



Maceration (a prefixation process) 



There are occasions when tissues are extremely dense and cannot be 

 manipulated while in fresh condition. It may be desirable to separate 

 the individual fibers of a muscle or nerve, and this is simplified by mac- 

 eration. The fluids used are not fixing solutions, so maceration usually 

 must be followed by some form of fixation. The following are various 

 suggestions for macerating fluids. (Hale, 1958) 



1. 30% alcohol, 24 hours or longer (3-4 days). 



2. formalin, 1 part in 10% salt (NaCl) solution, 100 parts: 24 hours or 

 longer. 



3. 10% sodium chloride: 24 hours or longer. 



4. chromic acid, 0.2% aqueous: 24 hours. 



5. nitric acid, 20% aqueous: 24 hours. 



6. boric acid, saturated solution in saline (sea water for marine forms), 

 plus 2 drops Lugol's iodine solution (page 410), each 25 ml.: 2-3 days. 



7. potassium hydroxide, 33% aqueous. Good for isolation of smooth 

 and striated muscle. After 1-1 1/4 hours, tease apart with needles. 



