CHROMO-ACETO-OSM10 ACID. 23 



tained with this mixture when it is allowed to act for only a 

 short time (about half an hour) . 



But it may, without inconvenience, be allowed to act for 

 many hours or even days. Wash out, very thoroughly, in 

 water. Stain with hsematoxylin, if you wish to stain in toto 

 (staining in this way with other reagents is possible, but very 

 difficult, and not to be recommended). Stain sections with 

 safranin, or other anilin, or with hsematoxylin or Kern- 

 schwarz. 



To make up this mixture with the usual stock solutions, you 

 take : 



Chromic acid of 1 per cent. . . 25 volumes 

 Osmic acid of 1 per cent. . .10 

 Acetic acid of 1 per cent. . .10 

 Water . . . . . . 55 



If you keep your osmium in 2 per cent, solution in chromic 

 acid of 1 per cent., as I have recommended, you will have to 

 take only 20 vols. of chromic acid, 5 of your osmium solution, 

 and 65 of water. 



It has been already stated more than once that Flemming's 

 solution is probably the very best fixing reagent in general 

 yet discovered. It has, however, been criticised. Faussek 

 (Zeitschr. f. wiss. Zool., Bd. xlv, 1887, pp. 694, et seq.) found it 

 totally inapplicable to the histology of the intestine of insects. 

 He states that it caused the intima to disappear, and the cells 

 to run together into a compact mass. Arnold (Arch.f. Mik. 

 Anat., Bd. xxx, 1887, p. 205) states that it does not preserve 

 cell-bodies faithfully. And A. Kotlarewsky (Mitth. d. naturf. 

 Ges. Bern., 1887; cf. Zeit. f. wiss. Mik., iv, 3, 1887, p. 387) 

 found that it preserved the forms of nerve-cells (spinal ganglia) 

 less faithfully than any of the reagents tried. I have not, 

 myself, been struck by any decided defect in the preservation 

 of cystoplasmic structures in my preparations made by this 

 reagent, but think it possible that the observations of these 

 authors may be well founded as regards the present formula, 

 but take it that that is merely a reason for preferring the 

 stronger mixture set forth below. 



It is not necessary in all cases to observe the exact proportions of the ingre- 

 dients in this mixture. FOL (Lehrb. d. vergl. Mik. Anat., 1884, p. 100) re- 

 commends the following : 



