FIXATION 723 



Muscle fibers isolated in this way may be kept for months or even 

 years. 



Caustic potash (potassium hydroxid) is also a valuable dissociator 

 for muscle tissue. The solution commonly used is made by dissolving 

 40 grams of the potash in 60 c.c. of water. Cardiac muscle is suffi- 

 ciently macerated in twenty minutes. The tissue must then be thor- 

 oughly washed, and may be preserved in the alcohol-glycerin mixture. 



Epithelium may be dissociated by teasing or by the action of a 40 

 per cent, solution of potassium hydroxid, or by means of a 10 or 20" 

 per cent, aqueous solution of 'lysol,' and preserved, if desired, in the 

 mixture of alcohol, glycerin, and water. 



Nerve cells may be isolated from the anterior horns of the spinal cord 

 or other gray matter of the central nervous system by teasing. They 

 may also be isolated by immersion in a 0.2 per cent, aqueous solution 

 of formalin in normal salt solution for two to twenty-four hours, or in 

 a 0.2 per cent, aqueous solution of potassium bicarbonate, two to five 

 days. Afterward they are transferred to a normal saline solution or to 

 a mixture of alcohol, glycerin, and water, and isolated by shaking, 

 assisted, if necessary, by gentle teasing. 



Similar preparations may also be made by placing small fragments 

 of tissue in 30 per cent, alcohol (Rauvier's alcohol; 2 parts water, 1 

 part 95 per cent, alcohol) for two days or more; then shake thoroughly, 

 allow the debris to settle, remove a drop of the fluid with a pipette, and 

 examine. 



For the isolation of the elements of the epidermis, hair and nails, 

 stronger solutions are required. Concentrated sulphuric acid may be 

 employed. After maceration is complete, the cells must be thoroughly 

 washed in water and may then be preserved in the alcohol-glycerin 

 mixture. A caustic potash solution, acting for two to three hours, is 

 also serviceable with these tissues. 



Any of the above preparations may be stained by the addition of a 

 small drop of a solution of eosin, picrocarmin, or methyl green to the 

 fluid in which they are examined. 



FIXATION 



For the preservation of tissue, and as a preparation for further 

 manipulation, most tissues require to be 'fixed.' Innumerable formulas 

 have been advocated for this purpose, many of them having as their 



