ZOOLOGY AND BOTANY, MICROSOOPYj ETC. 851 



treatment, Weigert's logwood may be used in the ordinary manner. For 

 decolorizing these sections, or those prepared by the original method of 

 Weigert, the author proposes a new reagent, with the intent of quite remov- 

 ing the stain from the interstitial tissue, in order that this may be contrast- 

 stained. The blue-black sections are placed in water, to which some alkali 

 (1-2 cc. of lithia solution to 100 cc. water) is added if the preparation does 

 not seem stained a deep blue. From the water the sections are transferred 

 to 1/4 per cent, solution of permanganate of potash for 20-30 seconds. 

 They are nest washed with water, and then transferred to the following 

 acid fluid : — Oxalic acid, 1 part ; sulphite of potash (K2SO3) 1 part ; 

 aq. destil. 200 parts. In a few seconds the sections are sufficiently de- 

 colorized. They are then stained with Magdala red or eosin (4-5 minutes), 

 or still better, with picrocarmine or with acetic acid carmine. Should any 

 spots remain after the acid solution, the section must be returned to the 

 permanganate solution for a moment, and the process repeated. Should the 

 sections have been treated with copper, the medullary sheath becomes red- 

 brown in the acid solution, and accordingly requires an alkaline bath, or some 

 suitable afterstain, as malachite green. It is advisable that the perman- 

 ganate solution should be made fresh every time, and should be changed as 

 soon as it shows a trace of brown. So too the acid solution should be 

 promptly replaced by a fresh quantity directly it begins to act slowly. The 

 foregoing method of decolorizing has the disadvantage that each section or 

 preparation requires the greatest attention on the part of the operator. 



Exuer had treated osmic acid preparations of the central nervous system 

 with ammonia, and thereby brought out many very fine nerve-fibres. In- 

 stead of ammonia. Pal used the reagents in the foregoing logwood method. 

 But for the cortex he advises weak ammonia (0 • 1 cc. ammonia to 100 cc. 

 water). The procedure is as follows : — Very small pieces of brain are 

 hardened in 1 per cent, osmic acid for four to six days, the fluid being 

 changed daily. The piece is then washed with distilled water, laid in abso- 

 lute alcohol for one or two minutes, imbedded in celloidin and then in wax 

 or paraffin, and then sectioned. The sections are removed from the knife to 

 pure glycerin, or diluted with 1/4 water. Therein they may be allowed to 

 remain for a length of time, but when required for use the glycerin must be 

 thoroughly removed. The sections are then removed with 1/4 per cent, of 

 permanganate solution for ten to fifteen seconds, after which they are trans- 

 ferred to the acid solution. The sections having been carefully washed, are 

 then stained again with some red dye (Magdala red, neutral picrocarmine, 

 acetic acid carmine). Mounting may be done in glycerin, or after dehydra- 

 tion and clearing up, in xylol or creosote in dammar. 



Staining Tubercle Bacilli.* — The contribution of Dr. P. Ehrlich on 

 staining tubercle bacilli is chiefly occupied by problematical doctrines about 

 the capacity of the bacterial envelope for taking up dyes. These doctrines 

 simply amount to the well-known facts that alkalis, anilin, and phenol 

 render the envelope more penetrable to stains, that mineral acids penetrate 

 relatively slowly, and that the membrane, when under the influence of 

 acids, is quite impenetrable to the compound molecules of the ordinary 

 dyes. 



The author's hints on practice are more valuable than his theories. 

 Thus he remarks that contrast stains, such as Bismarck brown for methyl- 

 violet, and methylen-blue for fuchsin, should be slightly acidulated with 

 acetic acid. 



* Charite'-Aimalen, 1886. Cf. Zeitsch. f. Wiss. Mikr., iii. (1886) pp. 52530. 



