26 FIXING AGENTS. 



and 65 of water. See also the remarks on the deterioration 

 of these solutions by keeping, in the next . 



It has been already stated more than once that Fleinming's solution is, 

 with the exception of Hermann's solution, probably the very best fixing re- 

 agent in general yet discovered. It has, however, been criticised. Faussek 

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

 applicable 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 iny prepara- 

 tions 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 in- 

 gredients in this mixture. FOL (Lehrb. d. vergl. mik. Anat., 1884, p. 100) 

 recommends the following ; 



1 per cent, chromic acid 25 vols. 



1 per cent, osmic acid 2 



2 per cent, acetic acid . ... . . 5 



Water . 68 



That is to say, a mixture much weaker in osmium than Flemming's. In 

 the Traite des Methodes Techniques, &c., Lee et Henneguy, 1887, I recom- 

 mended this mixture, as giving better results in general, but am now inclined 

 to think that, at all events as regards fidelity of fixation, it is a step in the 

 wrong direction, and that, on the contrary, the stronger mixture of Flemming 

 (next ) is a step in the right direction. Fol's formula has the advantage 

 of allowing better staining with carmine, that is all. 



A mixture still weaker than this in osmium, viz. with 1 vol. osmium solu- 

 tion instead of 2, has been recommended by GOBI (Zeit.f. wiss. Mik., vi, 1, 

 1890, p. 441), but I still adhere to the opinion above expressed. 



36. Chromo-aceto-osmic Acid (FLEMMING, SECOND or STRONG 

 formula, Zeit.f. wiss. Mik., 1, 1884, p. 349). 



1 per cent, chromic acid . .15 parts. 



2 per cent, osmic acid . 4 

 Glacial acetic acid . . 1 



If 2 per cent, osmium solution should not be at hand, you may con- 

 veniently make the mixture by taking 



10 per cent, chromic acid . . . .15 parts. 



1 per cent, osmic acid 80 



Glacial acetic acid 10 



Water 95 



