ZOOLOGY AND BOTANY, MICBOSCOPY, ETC. 1055 



hydrochloric acid. Wash carefully ; immerse in safranin for 10 to 20 

 minutes, and if possible in the warm. Dehydrate in methylated spirit, and 

 then decolorize in a mixture of oil of cloves (2 parts) and cedar oil 

 1 part. Then immerse in xylol until the right hue is attained. (See this 

 Journal, 1886, p. 899.) 



Congo-red as a Eeagent for Free Acid,*— Herr C. Wurster has 

 shown by experiment that Congo-red, when used for organic substances, is 

 not a certain test of free acid. In the presence of ammonia it forms with 

 this a compound which is not decomposed by organic acids at all and not 

 readily by inorganic acids (carbonic, acetic, hydrochloric, sulphuric, &c.). 

 The blue-violet colour which shows the presence of free acids, does not 

 occur in the presence of ammonia, when organic acids are added, or on 

 addition of inorganic acids when all the ammonia has been combined 

 with the free organic acid. 



Since in animal chemistry, ammonia in many cases can scarcely be 

 excluded, the yellow-red coloration of Congo-red may remain persistent 

 in spite of the presence of relatively large quantities of acid. 



Absorptioii of Anilin Pigments by living Animal Cells-t— The 

 results of the experiments made by Dr. G. Martinotti on the absorption 

 of anilin dyes by animal cells differ in some particulars from those of 

 Pfeffer, &c., who experimented in the same direction. It is found that 

 living animal or vegetable cells, if made to live in a medium coloured 

 with these pigments, are variously affected ; that is, that certain of these 

 dyes are more poisonous than others, a result which is reckoned by the 

 more or less rapid staining of the nucleus ; for when the nucleus becomes 

 visible by being stained, this indicates that the cell is dying or dead. If, 

 however, a quantity of pigment short of being poisonous be used, the 

 protoplasm of the cell becomes stained. But according to the author, 

 this quantity is, certainly for certain dyes such as methyl- violet, methyl- 

 green, &c., infinitesimal, and he only found two, Bismarck-brown and 

 methylen-blue, to give satisfactory results. 



If tadpoles be placed in a very dilute solution of Bismarck-brown they 

 take on a brownish-yellow colour in 24 hours, while the water has lost all 

 its colour. And if the solution be renewed from day to day, they may 

 finally be made to assume a yellowish-black hue characteristic of the dye. 

 Again, if they be placed in pure water, all the absorbed dye may be 

 gradually removed. 



Microscopical examination showed that certain kinds of cells only 

 possessed the power of selecting the pigment. These were the pigmented 

 cells of the skin within which the dye collected in such a way as to com- 

 pletely conceal their shape. Other cells which were red stained were the 

 branched connective tissue cells lying in the subcutaneous stratum. 

 Certain other polygonal epithelioid cells were found to contain large 

 well-stained granules in their protoplasm. In muscular fibre cells, in the 

 walls of blood-vessels, its coloured granules were occasionally seen. 



The action of methylen-blue was similar, but less active and less 

 pronounced. While the animal was alive the author did not find that 

 the axis-cylinder was stained, as Ehrlich did. With methylen-blue 

 certain granules normally found in the red corpuscles assumed a 

 deep blue colour. 



With regard to the absorption of these dyes during cell-prolifera- 



* Centralbl. f. Physiol., 1887, p. 240. 



t Zeitschr. f. Wiss. Mikr., v. (1888) pp. 305-13, 



4 B 2 



