1060 SUMMARY OF CURRENT RESEARCHES RELATING TO 



to these dyes, finding that only between the combinations of simple iodine 

 with rosanilin on the one part, and with the pararosanilin on the other part, 

 do the characteristic differences in the staining of the lepra bacillus exist. 



He suspects, therefore, that the iodine in pararosanilin staining com- 

 pletely extracts the dye where it is more loosely associated with the tissue, 

 and where the combination is stronger it unites with it in the tissue. A 

 new dye is therefore formed, which, on account of its slow and difficult 

 extraction, is more suitable to show further differences of the tissues than 

 the simple dye. The methods of Gram, Lutz, and Unna are accordingly to 

 be considered as variations of a general iodine-pararosanilin method. 



Extract of Logwood as a substitute for pure Haematoxylin.* — Dr. J. 



Paneth finds that the commercial extract of logwood is a satisfactory substi- 

 tute for pure hematoxylin in staining the central nervous system after 

 Weigert's method. From this extract is made a solution which contains 

 90 parts water, 10 parts spirit, 1 part dye. Before use it is filtered. To 

 100 ccm. of this solution 8 drops of a concentrated solution of lithium car- 

 bonate are added. The celloidin-imbedded sections are placed for twenty- 

 four hours in Weigert's copper acetate solution, then in 80 per cent, spirit ; 

 then are stained in the above solution for 18-24 hours at the ordinary tem- 

 perature. They are next decolorized with the borax and ferro-cyanide solution. 

 This method, which is practically that of Weigert, gives similar results, 

 but at a much less cost. 



Reduction of Chromic Solutions in Animal Tissues corrected by 

 Reoxidation with HgOa-t — It is well known that the brownish-green colour 

 assumed by animal tissues under exposure to chromic solutions is due to a 

 combination of the oxide of chromium (Cr203) with CrOs. There is a partial 

 reduction of the chromic acid in the tissues, resulting in the formation of 

 CrgOg, which then unites with the remaining CrOg to form the compound 

 known as chromic chromate. Dr. P. G. TJnna has shown that the greenish 

 colour can be removed by treating the tissues with hydrogen dioxide. 



The chemical processes involved are explained in the following manner : 

 — If a solution of chromic acid or bichromate of potassium be mixed with a 

 solution of H2O2, a deep green precipitate of chromoxide (CraOg) is imme- 

 diately formed, which combines with the remaining chromic acid to form 

 the intermediate salt (chromic chromate) with a brownish-green colour. If 

 the mixture is left to itself, the process of reduction, after reaching a definite 

 point, changes to one of oxidation, and the chromic chromate is soon reoxi- 

 dized, leaving the solution yellow as at first. The same phenomenon is seen 

 when (1) sections coloured by chromic acid or bichromate of potassium are 

 placed in H2O2, or when (2) sections treated with H2O2 are immersed in the 

 chromic solutions. The sections at once become dark green, then brownish- 

 green, and finally, in the first case yellow, in the second colourless. If the 

 sections, at the moment when the brownish-green colour appears, are removed 

 from the solution and thoroughly washed, the colour of the chromic chromate, 

 which is not unimportant for many histological details, remains fixed. 



Babes, — Nouvelle coloration des tissus normaux et pathologiques. (New stain for 

 normal and pathological tissues.) Bull. 80c. Anat. Paris, XI. (1886) p. 73. 



Hausee, G. — Zur Sporenfarbung. (On spore-staining.) 



Munch. Med. Wochenschr,, 1887, p. 654. 

 Joseph, M., and C. Wuester. — Tiber der Metapbenyldiamin als Kemfarbemittel. 

 (On metaphenykliamin as a staining agent for the nucleus.) 



Monatschr. f. prakt. Dermatol., 1887, Nr. 6. 



* Zeitschr. f Wiss. Mikr., iv. (1887) p. 213. 



t Arch. f. Mikr. Anat., xxx. (1887) p. 47. Cf. Anier. Natural., xxii. (1887) p. 



