AQUEOUS AMMONIA-CARMINE. 79 



may be to some extent prevented by means of antiseptics^ 

 as lias been proposed by Hoyer, who recommends the addition 

 of 1 to 2 per cent, of chloral hydrate. But it is now generally 

 recognised that it is better to allow the whole series of changes 

 to take place, not using the solutions until the changes have 

 been entirely accomplished. Such solutions, known as " aus- 

 gefaulte Carmin," "carmin pourri," putrefied carmine, are 

 greatly superior in staining power to solutions in which these 

 changes have not taken place. It has been proved by G-IERKE 

 (Zeit. f. wiss. Mik., i, 1884, p. 76) that they owe this enhanced 

 power to the presence of traces of carbonate or bicarbonate 

 of ammonia, which is formed in the solutions by the combina- 

 tion of their free ammonia with the carbonic acid of the air. 

 It has been demonstrated that these carbonates act as mor- 

 dants in the staining process. 



The solutions thus prepared form an exception to the state- 

 ment made above ( 131) that carmine is of little good for 

 staining sections, inasmuch as they give one of the best stains 

 known for sections of the central nervous system. 



136. Aqueous Ammonia- Car mine (BETZ, Arch. mik. Anat. ix, 

 1873, p. 112). Commercial carmine is rubbed up with a little 

 water in a mortar until a thick syrupy mass is obtained ; on 

 to this ammonia is poured, with continual stirring. The solu- 

 tion is diluted with a large quantity of water, and filtered. 

 The filtered solution is exposed to the sun in an uncorked 

 vessel, which must be of green glass, until a dirty red, floccu- 

 leiit precipitate appears ; it is then filtered. The solution is 

 again left to stand in the same conditions as before, and when 

 the precipitate reappears, it is again filtered, and the solution 

 again exposed. Generally no third precipitate appears ; if it 

 does, filter again. In either case, the preparation is now 

 finished, and the solution is to be preserved for use in a 

 corked vessel. It will keep for months. It sometimes hap- 

 pens that the solution whilst exposed to the sun acquires a 

 bad smell, and becomes covered with a white flocculent mem- 

 brane. This does not hinder the preparation, but, on the con- 

 trary, furthers it. 



For sections of nerve-centres liiilt' ;m hour, or at most an 

 hour, suffices to stain sections. The first elements that stain 

 are the granular mass of the grey matter, then nerve-cells, 



