CHAPTER XVII. 



LABORATORY DIRECTIONS. 



PREPARATION OF MATERIAL. 



I. Spreads. Thin spreads or smears are made 

 upon cover glasses or on glass slides. The specimens 

 are then studied, stained or unstained, but always 

 in some liquid medium. They may be fixed and 

 mounted permanently by treating the preparations 

 just as if they were sections. Blood, marrow, nerve 

 cells from brain or cord, and scrapings from organs : 

 as the liver, may be prepared in this way. 



II. Teasing. Muscle, tendon and nerve fibers are 

 easily prepared in this way. The teasing, or spread- 

 ing, may be done in water and glycerin, or small 

 pieces may be dehydrated with alcohol and then 

 teased in oil, or even in balsam, thus making a per- 

 manent mount. Alcohol and oil harden the tissues, 

 and satisfactory teasing is therefore more difficult. 



III. Dissociation or Maceration of Tissue Ele- 

 ments 



1. Alcohol, 25 per cent.; time, twenty-four 



or forty-eight hours. 



2. Strong acids, as hydrochloric or nitric; 



time, twenty-four hours. 



3. Caustic potash, 25 per cent.; time, ten 



to thirty minutes. 



To obtain columnar and goblet cells of the intestine, 



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