ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 709 



Staining.* — Prof. M. Flcscli considers the action of staining 

 media ; first the inorganic, and secondly the organic. 



The action of the inorganic salts, silver, gold, iron, may bo 

 summed up by saying that the various appearances produced by 

 metallic impregnation are to be explained partly from the physio- 

 logical condition of the material examined, partly from various 

 chemical affinities to particular tissue elements, and partly to differ- 

 ences in physiological constitution. As examples of the foregoing 

 he gives two illustrations of specimens treated with silver nitrate, 

 one showing a section of cartilage of frog silvered en masse with a 

 weak solution of silver nitrate, and the other giving the appearances 

 of quite fresh cartilage of frog silvered in section with the same 

 solution. The differences between the results are to be explained by 

 the greater imbibition capacity of the second kind, and are not to be 

 attributed to chemical differences. 



The effect of au organic stain is produced either by chemical 

 combination or by surface attraction, i. e. by mere adhesion or in- 

 filtration of the stain without chemical union. Examples of tho 

 former are to be found in safranin, methyl-violet, &c, in their action 

 on amyloid substance ; in borax-carmine on haeniatoxylin ; in Merkel's 

 stain for the salivary ducts. An intermediate variety, one consisting 

 partly of infiltration and partly of chemical union, may be found in 

 neutral litmus solutions which stain the cell-substance red and the 

 nuclei blue. 



The action of infiltration is dismissed in a few words, as Giei-ke's 

 published researches have anticipated further remarks. Dr. Flesch, 

 however, urges that the hardening process must count for something 

 in the result of staining processes, and concludes his paper by insisting 

 on the significance of a physical characteristic — the unequal suscepti- 

 bility for imbibition of the tissues and their elements — and the 

 influence of the fixative changes on this susceptibility from imbibition 

 of organic material. 



Weigert's Hematoxylin Stain for the Central Nervous System. — 

 Prof. M. Flesch in some comments | on his experience with Weigert's 

 method says that preparations which have been washed in water in 

 the usual way, after coming from Mailer's fluid, can be stained, pro- 

 vided the sections (made in celloidin) are treated a few minutes in 

 1/2 per cent, solution chromic acid, and then, after being washed in 

 water, placed in the colouring fluid. The sections stain very much 

 quicker than by Weigert's method. The decolouring process of 

 Weigert is followed. Creosote is decidedly preferable to xylol as a 

 clarifier. 



According to Dr. C. S. Minot,J Weigert's hematoxylin method 

 may be used after any method of hardening and cutting, provided the 

 sections are treated 5-15 minutes in 1 per cent, bichromate of potas- 



* Zeitschr. f. Wisa. Mikr., ii. (1885) pp. 4G4-77 (2 figs.). 

 t Ibid., i. (1S84) pp. 564-6. 



X ' Whitman's Methods in Microscopic.il Anatomv and Embryology,' 18S5, 

 p. 192. 



