AS TO PICRO-CARMINE. 81 



141. Hoyer's Neutral Carmine (Biol. Centmlb., ii, 1882, p. 17j. 

 If the solution made by the process given supra, 138, be 

 mixed with 4 6 times its volume of strong alcohol a scarlet- 

 red precipitate is formed. This is separated by filtration, 

 washed, and dried, or made into a paste with alcohol in which 

 some glycerin and chloral is dissolved. Both the powder and 

 the paste can be kept several months unchanged ; they dis- 

 solve easily in water, particularly the paste. The solution 

 passes readily through the filter, whilst the ordinary carmine 

 solution can only be filtered with difficulty ; it also keeps a long 

 time unchanged, especially with the addition of 1 2 per cent, 

 of chloral, and it has a much more intense colouring power. 



" By dissolving the carmine powder in a concentrated solu- 

 tion of neutral picrate of ammonia a combination is obtained 

 which has all the advantages of ordinary picro-carmine with- 

 out any of its disadvantages." 



142. Bonn's Neutral Carmine (Arch. Anat. u. Phys. (Anal. Abth.), 

 1882, p. 4). Three to 4 grms. carmine are rubbed up in a mortar with 200 

 grms. water, and ammonia is added drop by drop until the solution acquires 

 a cherry-red colour ; acetic acid is then added until the colour becomes of a 

 sealing-wax red ; and the solution is filtered. If the colour is not intense 

 enough, add before filtering two drops of ammonia, and leave in an open vessel 

 until the smell of ammonia can no longer be perceived. 



Tissues should remain for twenty-four hours in the stain (or longer if they 

 are more than 1 mm. thickness), after which it is desirable, in order to ensure 

 a nuclear stain, to wash out with glycerin and water (equal parts) containing 

 per cent, of hydrochloric acid. 



These directions apply to blastoderms. 



This formula has been erroneously attributed to " Bohm " by more than 

 one writer. 



143. Heidenhain's Neutral Carmine (Arch.f. mik. Anat., vi, 1870, 

 p. 402.). (Beale's carmine, without the alcohol, and neutralised.) 



144. As to Picro-Carmine. By the term " picro-carmine " 

 there ought to be understood a definite chemical substance, a 

 double salt of picric and carminic acid and ammonia. It is 

 commonly used to denote a whole tribe of solutions in which 

 carmine, ammonia, and picric acid exist uncombined in hap- 

 hazard proportions. In the face of this confusion, all that can 

 be done is to distinguish the true picro-carmine as " Ranvier's " 

 picro-carmine, or picro-carminate of ammonia. 



True picro-carmine is one of the most important of the car- 

 mines. It gives very delicate differentiations, and has the 



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