ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 773 



anilin dyes, such as toluidin blue and Unna's polychrome methylen- 

 blue With toluidin bine he applied a mordant, using either ammonium 

 molybdate, after Bethe, or antimonium tartrate (tartar emetic) according 

 to Schuberg. With this method he could demonstrate the nerve 

 fibrillae ; he used as a control stain the iron-hsematoxylin method of 

 M. Heidenhain, after which he stained with a 1 p.c. aqueous solution 

 of acid fuchsin, and obtained a most useful appearance ; also R. Heiden- 

 hain's stain with aqueous hematoxylin and a subsequent mordant of 

 chromate of potash gave good results ; he also obtained good prepara- 

 tions of very thin sections with the iron-hsematoxylin method of Butschli 

 — acetate, iron oxide, and aqueous hematoxylin. Sections of :3 p or 

 less were only obtained if the retina had been separated from the under- 

 lying thick layer of connective tissue before imbedding. To obtain 

 thin sections of the retina in conjunction with the connective tissue he 

 employed Mastix collodion after Heider. 



To bleach the pigments he used a mixture of 85 parts of 96 p.c. 

 alcohol and 15 parts of nitric acid, and a knife's-pointful of KC1 or 

 KC10 3 , care being taken that the object does not remain for long in 

 contact with the KC1 or KC10 3 , lest the tissue be destroyed. 



For fixing the eyes of the Dibranchiates he found Zenker's mixture 

 was especially good. For staining he used Heidenhain's iron-haema- 

 toxylin combined with acid fuchsin or orange ; and besides these he 

 used Blockmann's fluid that stains the nerve fibres pale yellow, the 

 other constituents staining blue, and he obtained excellent results by 

 combining this reagent with borax-carmine, osmium, and wood-vinegar. 



Theory of Vital Staining.* — Y. Ruzicka, as the result of extended 

 research, has elicited a difference in the staining relations of living and 

 dead protoplasm, living protoplasm staining red, dead protoplasm 

 staining blue, when treated with an equimolecular mixture of neutral 

 red and methylen-blue. The method consists of mixing equal parts of 

 • 05 p.c. solution of neutral red and methylen-blue in distilled water ; 

 some of the mixture is dropped on a clean slide and allowed to evaporate 

 at 85° C. in the incubator ; on to the dried layer of stain is brought 

 the object in the same isotonic medium, which serves equally as a 

 solvent for the stain mixture. In seeking to explain his results the 

 author considers that living substances exist in a more or less fluid con- 

 dition, and consist of two layers of different densities, an outer denser 

 and an inner more fluid ; and he conceives that when such a cell is 

 surrounded by fluid its outer layer would behave, in respect to the 

 separate fluids, as a membrane ; and, assuming that the staining process 

 proceeds according to the laws of simple diffusion, and will continue 

 until the concentration of the fluids on either side of the membrane are 

 equal, a mixed violet tone would result. But as this does not occur, he 

 concludes that his results do not admit of a simple physical explanation. 

 The author suggests two other explanations : either the methylen-blue 

 cannot penetrate into the living cell because the outer cell layer opposes 

 an insuperable barrier to its molecules (but this is not tenable, for 

 living cells can be stained well by methylen-blue) ; or it is possible that 



* Zeitschr. wiss. Mikrosk., xxii. (1905) p. 91. 



