172 PRACTICAL HISTOLOGY. 



may yield excellent results, it is very uncertain in its opera- 

 tion. Tardiness and uncertainty of action may be avoided 

 by retaining all the ammonia in the fluid, and by diluting 

 the fluid when it is to be used. Therefore, prepare the 

 fluid thus : Place the carmine in a test tube, add the 

 ammonia, bring to the boiling point, add the water and 

 filter, then add the spirit and glycerine, and preserve in a 

 stoppered bottle. When about to be used it should be 

 diluted from two to seven times with water. The last is 

 the most generally useful dilution. The fluid should always 

 be filtered after dilution, and the tissues placed in a large 

 quantity of it from 2 to 24 hours. This fluid is therefore 

 not at all suitable for rapid staining, but carmine staining 

 is generally most beautiful when it takes place slowly. 



b. Strong carmine fluid. It is useful to have a strong 

 carmine fluid for rapidly staining nerve tissues. It is thus 

 prepared : 



Carmine i gramme. 



Strong ammonia . . iCC. 

 Dissolve in a test tube, with the aid of a gentle heat, and add 



Distilled water . . 2300. 



Filter and preserve in a stoppered bottle. For ordinary 

 purposes it tinges too rapidly, and for tissues unhardened 

 in chromic acid or Miiller's fluid it contains too much 

 ammonia. Therefore, should this fluid be used for staining 

 in the ordinary way, expose it in a beaker to the air for 

 two days, to let the excess of ammonia escape, then dilute 

 it with five times its bulk of distilled water, filter, and pre- 

 serve in a stoppered bottle. 



319. Carmine staining with palladium. When tissues, 

 and especially nerve tissue, have been overhardened in 

 chromic acid, carmine may entirely fail to stain them. In 

 such a case the following method (Merket) is of much service. 

 Place a large drop of J per cent watery solution of palladium 

 chloride on a slide, and on another slide a large drop of a 

 strong ammoniacal solution of carmine ( 318, b\ Allow 

 the section to remain in the palladium for about two 

 minutes. Wash it in water and place it in the carmine 

 fluid for about three minutes. Then wash in water. 



