vi ALBUMIN-DYE COMPOUNDS 227 



but as soon as the reaction of the fluid is rendered slightly alkaline 

 with sodium carbonate, then an insoluble lead-albuminate is thrown 

 down. As gelatine and protamin-solutions are not precipitated under 

 the same conditions, and as they are deficient in the phenol group, it 

 follows that in albumin and similarly constituted proteids the basic 

 lead radical must join on to the ' acid hydroxyl ' radical of the phenol. 

 Colour-bases used by histologists are neutral salts, being generally the 

 chlorides, hydrochlorates, etc., and react as does lead acetate. Thus, 

 on bringing together a solution of basic-fuchsin, methyl-green, thionin, 

 toluidin-blue, safranin, or other basic stains (" with the possible excep- 

 tion of vesuvin," which contains a mixture of colour acids and colour 

 bases) with a solution of an albumose, nothing happens ; but if a 

 similar albumose solution be rendered slightly alkaline with sodium 

 carbonate, then a " flocculent, coloured precipitate, consisting of the 

 albumose in combination with the dye, is thrown down." 



" These experiments prove that many of the basic dyes enter into 

 chemical combination with the albumose molecule when in alkaline 

 solutions, forming insoluble coloured compounds," and "reacting in 

 this respect like basic lead acetate, protamin, histone, or other organic 

 bases. . . . Basic dyes in alkaline solutions may thus be used for the 

 detection of albumins in the cell, and indeed of albumins possessing a 

 phenol or tyrosin group." It is thus beyond all doubt that ordinary 

 colour acids and colour bases will combine under suitable conditions 

 with albumins and albumoses to form definite salt-like compounds. 

 The behaviour of dyes towards coagulated proteid has been also 

 carefully studied by Mathews, but the reader is asked to consult 

 either the original paper by Mathews or the abstract in the author's 

 Physiological Histology, 1902, pp. 349-51. 



Nietzki, in the last edition of his Chemistry of Organic Dyes, says 

 in 1901 : "Certain facts speak for the view that the union of dyes 

 with fibres is a salt-like union, in which the fibre, analogously to an 

 amino-acid, plays in the one case the part of an acid, in the other 

 case that of a base. Thus rosaniline in the form of its free base 

 (carbinol base) is colourless while its salts are coloured. If a skein of 

 wool is placed in the colourless solution of the colour -base and the 

 solution is then heated, the skein will be stained as intense a red as 

 if the corresponding amount of rosaniline hydrochlorate or other 

 rosaniline salt had been used." " The fibre in this union plays the 

 part of an acid." " That the fibre may play the part of a base towards 

 a colour acid is shown in a very instructive manner by the quinoid- 

 ethylether of tetrabrome-phenol-phthalein. This ether in the free state 

 is pale yellow, and dilute solutions appear almost colourless, while its 



