MICROSCOPICAL TECHNIC 433 



THE TISSUE ELEMENTS IN THEIR RELATION TO FIXATIVES 



AND DYES. i 



With iodin-potassium iodid solution, starch grains give a blue 

 adsorption compound (see p. 135). 



Glycogen forms with it a red adsorption compound. The stain 

 with strongly alkaline potassium carmine recently recommended by 

 BEST is so complicated that it cannot yet be interpreted. 



The Lipoids. 



The fixation and staining of lipoids can hardly be regarded as 

 other than a colloid-chemical question. Fixation is generally ac- 

 complished with osmic acid by means of which the fat is simultane- 

 ously blackened and the acid is reduced to colloidal metallic osmium; 

 similarly, gold, silver and palladium salts are reduced to the colloidal 

 metal. Of the true dyes, we must especially consider those which are 

 very soluble in fat, though quite indifferent chemically, and which 

 are very slightly adsorbed by the other constituents of the cell. 

 Among these are Scarlet R (fettponceau) and Sudan III. Both are 

 amphoteric dyes in which the basic as well as the acid character is so 

 indefinite that they seem quite indifferent and do not form salts with 

 aqueous caustic soda. Employed in alcoholic solution, staining 

 results. 



Protoplasm. 



We may attribute to protoplasm chemical properties similar to 

 those of the albumins. Protoplasm may be amphoteric, on which 

 account neither acid nor basic properties become more prominent. 

 Consequently, protoplasm stains only faintly with either basic or 

 acid dyes, even though its water content is relatively high. 



Nucleus. 



The chief constituents of the cell nucleus are the nucleoproteins. 

 These are strongly acid in character; to them may be attributed the 

 intense staining of the nucleus with basic dyes, and to them the in- 

 tensely staining constituent of the nucleus is indebted for the name 

 chromatin or chromatic substance among histologists. The union with 

 the color base becomes firmer with the lapse of time, since in the 

 beginning it is possible to effect almost complete decolorization with 

 alcohol, whereas when the dye acts for a longer period the nuclei 

 retain their intense staining and only clouds of color leave. For 

 nuclear staining any basic dye may be employed; safranin, fuchsin, 

 methyl violet, methyl green and bismarck brown are recommended 

 most highly. 



