84 The Microscope. 



water occasionally during the boiling, to make up for the water lost 

 by evaporation. Cool, and pour without filtering into a ten- ounce 

 or larger bottle. Add the alcohol and let stand with occasional 

 shaking, for forty-eight hours. Filter and preserve in close 

 stoppered bottle. Carmine, thirty grains, can be used, if desired, in 

 place of the cochineal, and gives a nearly identical stain. There 

 is, however, no advantage in its use, and the cochineal is cheaper. 



The stain made as above is a perfectly clear, purplish-red 

 fluid, and is superior to any aqueous alum-carmine stain in the 

 clearness and brilliancy of the coloring which it imparts to the 

 tissues. It will keep indefinitely, but a slight precipitate sometimes 

 forms, which should be filtered out. This does not indicate any 

 decomposition of the stain, nor does it alter its staining character in 

 any respect. The following stain, made with carmine and without 

 heat, will give a fluid nearly identical with the first, except that no 

 precipitate ever occurs, however long it is kept: 



Carmine 30 grains. 



Alum 4 drams. 



Distilled water 4 ounces. 



95 per cent, alcohol 4 ounces. 



Grind the carmine and alum together in a mortar, gradually 

 adding the water. Add the alcohol, and pour without filtering into 

 a ten-oimce bottle, cork tightly and let stand for a week, shaking 

 occasionally. Filter, and preserve in a close -stoppered bottle. 

 When these fluids are used for staining in bulk, pieces of tissue can 

 be transferred directly to them from the strong alcohol in which 

 they have been preserved, to remain from two days to as many 

 weeks, according to the size of the piece and the previous treatment 

 of the tissue. Tissues hardened in alcohol, or corrosive sublimate 

 and alcohol, stain much more rapidly than those hardened in 

 Muller's fluid or chromic acid. In all cases in which a fluid for 

 hardening other than alcohol is used, it should be entirely removed 

 from the tissue by repeated changes of alcohol, before the stain is 

 applied. In fact, this should always be done, tvhatever stain is to 

 be employed, and whether the staining is to be done in bulk, or 

 after sectioning. Overstaining need not be feared with any of the 

 alum-carmine fluids, and the tissue should always remain in the 

 fluid long enough to ensure the penetration of the stain to every 

 part. The length of time required for different tissues can only be 

 learned by experience, but to begin with, it is better to err on the 

 side of leaving the piece in the stain too long, than the reverse. 



