1885.] 



MICROSCOPICAL JOURNAL. 



67 



Notwithstanding the n u m e r o u s 

 staining preparations that have been 

 strongly recommended, some of 

 which are useful for special work, 

 such as the net-work of fibrill^e in the 

 gray matter, carmine is, in my opin- 

 ion, the best material for show- 

 ing white nerve substance, branching 

 cells, and neuroglia. This dye is ob- 

 tained from cochineal, which is the 

 dried female of a scale insect first 

 found in Central America. It is now 

 cultivated wherever the cactus on 

 which it feeds will grow. The in- 

 sects are boiled in a solution of cer- 

 tain salts, as alum or saltpetre. Each 

 maker has his own method, but only 

 the very best brands are suitable for 

 microscopy, that known as ' Naka- 

 rete ' being the best. The cochineal 

 solution is allowed to stand until the 

 carmine precipitates, when it is dried 

 in cakes. Chemically it is carminic 

 acid with the formula C ^ "^ H ^ ^ 

 O ^ . It is not soluble in water, but 

 combines with ammonia and acetic 

 acid, the first compound being tha- 

 most often used in staining. To set 

 cure the best results a strong solution 

 should be kept in stock ; that which 

 is freshly made seldom works so well, 

 and may contain free ammonia to its 

 injury. I pulverize the commercial 

 cubes, add water and sufficient am- 

 monia to dissolve it. I then allow it 

 to stand several days in an open ves- 

 sel ; then filter. This concentrated 

 solution I keep for about two years 

 in corked bottles before using if pos- 

 sible. All the ammonia will disap- 

 pear — part by absorption of carbon 

 dioxide, part by evaporation. The 

 presence of ammonium carbonate is 

 very advantageous ; it acts as a mor- 

 dant. One of the chief advantages of 

 carmine is that it works well whatever 

 the previous treatment of the prepara- 

 tion. Chromic acid has been said to 

 be incompatible, but it is not so unless 

 too strong, and for brain sections is 

 better than alcohol, the use of which 

 for them should be avoided even to 

 moisten the knife. Ammoniacal car- 

 mine is the most permanent dye 



known ; if properly used it never 

 fades. I have seen some of Gerlach's 

 preparations of the spinal marrow 

 twenty-five years old, that appeared 

 to be unchanged. None of the nu- 

 merous colors that have been tried 

 are entirely satisfactory in this re- 

 spect. Gold preparations darken, 

 vegetable dyes fode, though Hema- 

 toxylon with alum as a mordant is 

 the most desirable after carmine. In 

 1S56 a new class of dyes was intro- 

 duced, the anilines, that worked a 

 revolution in dyeing. The first was 

 Mauvein ; in 185S, Hofmann dis- 

 cov^ered anilin red, and many others 

 soon followed. Waldeyer was the 

 first to apply these in histology ; he 

 used rosanilin, anilin violet and anilin 

 blue. But the anilin colors have not 

 found favor yet as important stains. 

 Thiersch, in 1865, recommended 

 indigo-carmine and Chrzonszczewski 

 found it especially suitable for inject- 

 ing the tubuli of the liver and kid- 

 neys. 



About this time a great step for- 

 wards was made, viz., double stain- 

 ing. Picric acid and carmine v^^ere 

 used separately by Schwarz for this 

 purpose, and the publication of his 

 peculiar methods in 1867 undoubtedly 

 led Ranvier to the idea of combining 

 the two and making picrocarmine, 

 which remains one of our choicest 

 stains. A species of double staining 

 was however known before Schwarz, 

 made by impregnating tissues with 

 metals, then dyeing in carmine. Also 

 Schulze and Rudneft' in 1S66 used 

 osmic acid to darken sections sub- 

 sequently treated with carmine. This 

 brings me to another branch of the 

 subject, viz., impregnation with me- 

 tallic salts, which is quite as useful 

 as staining, and has been entirely 

 worked out since i860. 



The following historical synopsis 

 of literature on staining in Micro- 

 scopy contains all the important 

 original works, essays, and notices 

 on our subject. Those which are 

 simply repetitions or recommenda- 

 tions of earlier work are omitted. 



