420 HISTOLOGICAL TECHNIQUE. 



have lost all traces of a red tint. This washing may take several 

 minutes, or even a few hours ; but if good, permanent stains are 

 desired, it is of great importance that it be thorough. This wash- 

 ing completes the actual staining with hsematoxylin, and the sections 

 are then ready for counterstaining with eosin or for dehydration. 



The eosin solution used for diffuse staining is prepared by dis- 

 solving 1 gram of eosin in 60 cc. of 50 per cent, alcohol. Of this 

 solution, about ten drops are added to 5 cc. of distilled water in a 

 small dish ; the sections are stained for about five minutes and then 

 washed in distilled water. They are then ready for dehydration 

 and mounting. The diluted eosin should be thrown away after use, 

 but the hsematoxylin can be filtered back into the stock-bottle. 



Since the hsematoxylin solution improves with age, no exact 

 directions can be given as to the length of time sections should 

 remain in a particular solution. Three minutes will usually yield 

 good results ; but if it is found that the color is too dark, a shorter 

 time should be employed, and vice versd. One soon becomes famil- 

 iar with the staining-powers of the particular solution used. The 

 dishes that have contained ha?matoxylin should be washed soon 

 after use, or may be subsequently cleaned with a little hydrochloric 

 acid, all traces of which should then be removed by thorough wash- 

 ing in water. 



The above method for staining with hsematoxylin and eosin is 

 highly recommended for general routine work. 



2. Neutral Carmine. 



Carmine, "No. 40," 1 gram. 



Distilled water, 50 cc. 



Ammonia, 5 " 



The solution is allowed to remain exposed to the air until the 

 odor of ammonia is no longer perceptible. It is then filtered into 

 a bottle, where it is kept till needed. 



Neutral carmine gives a diffuse stain, resembling that of eosin, 

 but rather clearer in character. It is employed in a greatly diluted 

 form, according to the following directions : 



One drop of the neutral carmine is mixed with about 20 cc. of 

 distilled water. A trace of acetic acid is then added by dipping a 

 platinum needle into the acid and stirring the diluted dye with the 

 acidulated needle. A piece of filter-paper is then placed upon the 



