CHAP. VII.} PARAFFIN SECTIONING. 167 



stain like hydrochloric acid carmine, remove the slide from the alcohol, and add 

 the stain directly after draining the slide. Do not allow the stain to become dry, 

 for that would injure the tissue. Wash away the stain with 67% alcohol, then 

 dehydrate with 97% alcohol, clear and mount in balsam as described below. 



§ 279. Staining with an Aqueous Dye. — Wash away the 95% alcohol from 

 the slide bearing the sections by plunging it into a jar of water and moving it 

 around a moment. Then add the stain to the sections with a pipette, or immerse 

 the slide in a jar of the stain, and allow the stain to act from 5 to 10 minutes. 

 Wash thoroughly with water. 



\ 280. Staining with a General Dye — Counterstaining. — If it is desired to 

 give a general stain after the nuclear dye (§ 279), carmine stained preparations may 

 be tinted with picric-alcohol for half a minute or more (g 315), and the hematoxylin 

 stained specimens with eosin ( \ 305 ) . It usually takes less than a minute for this. 

 Wash away the counterstain with water. 



\ 280a. Counterstaining with Picro-fuchsin. — For a general dye to use with 

 hematoxylin, eosin is good, but to differentiate the tissues more completely, 

 especially connective tissue, which is present in practically every section made, it 

 is better to use Van Gieson's mixture of picric acid and acid fuchsin. (Picric acid, 

 saturated aqueous solution 75 cc, water 25 cc. 1% aqueous solution of acid fuchsin, 

 10 cc.) Sections are first strongly stained with hematoxylin, well washed with 

 water and then stained 3 seconds to 15 minutes in the picro-fuchsin. They are 

 then washed in distilled water or in tap water, to which has been added a drop or 

 two of glacial acetic acid to 100 cc. of the water. They are then dehydrated, 

 cleared and mounted in acid balsam, that is in balsam which has not been neutral- 

 ized ( \ 300). If glycerin or glycerin jelly is used as a mounting medium it should 

 be slightly acid. Unless the mounting medium is slightly acid, the red of the acid 

 fuchsin soon fades. In some cases less acid fuchsin should be used, and in some a 

 greater amount. Acid fuchsin alone without the picric acid is also good for a 

 counterstain. The picro-fuchsin is a very valuable differential stain and combined 

 in different proportions with picric acid will give great assistance in almost every 

 case. It does not seem to be a very permanent stain. (See Freeborn, Trans. N. 

 Y. Path. Soc, 1893, p. 73. Also studies from the department of pathology of the 

 College of Physicians and Surgeons, Columbia University, N. Y., 1894-1S95). 



\ 281 . Dehydration of the Stained Sections. — Place the slide with the stained 

 sections in a jar of 95 % alcohol and leave it a few minutes, or wave it around in 

 the alcohol for half a minute or so. 



\ 2S2. Clearing the Sections. — Drain off the alcohol, and place the slide in a 

 jar of clearer ( \ 303, A or B) or put a drop or two of clearer on the sections. The 

 clearing is usually accomplished in two or three minutes. 



\ 283. Mounting in Balsam. — For this the clearer is drained from the slide, 

 and wiped away with lens or blotting paper, cloth, etc. The balsam is then put 

 upon the sections and the cover added, or a cover-glass is spread with the balsam 

 and put over the sections. (If the sections show a whitish appearance and are 

 opaque they were not sufficiently dehydrated.) 



