Boil for twenty minutes. Filter. Add a few drops of carbolic acid.
In using this reagent it should be filtered into a watch glass, and the sections placed in it for at least an hour. There is no fear of overstaining, and they may be left all night. After they have been stained they must be thoroughly washed in water to remove the alum, otherwise numerous crystals of it will be seen in the field when the section is mounted. Sections may be mounted in Farrant’s solution or in Canada balsam. The staining effect improves very much after the section has been kept a few days.
If desired its staining action may be complemented by dehydrating it in an alcoholic solution, either of eosine (1 in 1500) or of picric acid, and then clearing up in oil of cloves, and mounting in Canada balsam.
By itself it gives a stain very like that of hæmatoxyline, only warmer. It picks out the nuclei and axis cylinders of nerves, stains cell protoplasm slightly, and the fibrous elements scarcely at all.
It may be used for the same purposes as hæmatoxyline. The colour is less attractive, and not so deep as that of the latter, but as it does not overstain sections, even when left in it for a week, it is a very convenient stain for general purposes.
It is particularly useful as a contrast stain for sections of brain and spinal cord, after the Weigert-Pal hæmatoxylin process (p. [88]).
Ammonia-picrocarmine was formerly very largely used as a staining reagent. Its place has now to a large extent been taken by lithio-picrocarmine.
In its preparation the best carmine must be used.
It is made as follows:—
| Carmine | 1 | part. |
| Liq. ammon. fort. | 3 | parts. |
| Distilled water | 3 | parts. |