Literary Notices. xli 



75 M. The best results were obtained by fixing as above, staining in one 

 half per cent, aqueous h:ematoxylin for one hour or more and decolorizing in 3 

 per cent, iron alum. This gives very brilliant Weigert preparations. 



This fixing fluid was devised and suggested to me by Dr. Oliver S. Strong, 

 who has applied it very successfully to the amphibian brain. The fixa- 

 tion is not so perfect as that of the osmic acid mixtures, but better than the 

 usual bichromate. Moreover, it has a very considerable decalcifying power, a 

 point of no small practical value. My specimens of young, but nearly full 

 grown, minnows were fully decalcified after 5 days' treatment. The stain is 

 absolutely differential, the ground both centrally and peripheralUy becoming al- 

 most perfectly transparent. All nuclei, however, resist the decolorizer more or 

 less, though usually not so much as the nerves. The latter are are of a very 

 brilliant light blue color, the dye being confined to the periphery and the axis 

 cylinder of the larger fibers, but staining all of the myelin of the smaller ones. 

 The sections are of exquisite beauty ; unfortunately, however, the fixer leaves 

 the tissue very brittle and of a very poor consistency for cutting. This is an in- 

 superable objection to its use in the study of the peripheral nerves, as I have 

 never been able to get satisfactory continuous sections through the whole head. 

 In the case of brain or spinal cord this disadvantage is not so serious.^ 



76 F. A small specimen was hardened for 8 days in the following mixture: 



Chrome alum, 4 per cent., 45 parts. 



Iron alum, 4 per cent., 45 parts. 



Formalin, 10 parts. 



It was then left in 10 per cent, formalin for a week and embedded and sec- 

 tioned. The sections were stained in aqueous hsematoxylin and decolorized in 

 iron alum, as in the preceding case. The fixation is about as before and the 

 stain very similar, though the ground does not clear well. Other decolorizers 

 were not tried. The tissue seems to be in much better histological condition 

 than that fixed in formalin and iron alum alone, and the method merits further 

 study. 



Summary. — None of the mixtures of formalin and the metallic 

 salts give wholly satisfactory results. Either the fixation is not perfect 

 or the tissue is of poor consistency for cutting. The most valuable 

 combinations which I have tried are mixtures of formalin and iron 

 alum and formalin, iron alum and chrome alum. These fluids fix well, 

 have considerable decalcifying power and yield the most brilliant sheath 

 stain (and the former the most transparent ground) which I have ob- 

 tained by any method. 



This pre-eminence of the iron alum as a mordant accords with 



^ Since the publication of this article Dr. Strong writes me that sections of 

 old embryos of the smooth dog-fish, Galeus cants, fixed in the iron-alum-for- 

 malin and stained without further mordanting in aqueous hematoxylin, decolor- 

 ized with I per cent, iron alum are very fine. The fixation is admirable, espec- 

 ially the connective tissue, which is perfect (probably due to the formalin). 



