MICR O CHEMIS TRY. 91 



Alcannin has also been much used (cf. 109) in the study 

 of the resins. Preparations treated with this stain do not 

 appear, however, according to the author's experiments, to 

 be capable of preservation in glycerine-gelatine. 



In connection with the resins may be mentioned the 

 following compounds not yet well studied macrochemically. 



a. Fungus-gamboge. 



146. Zopf (V, 53) denominates as fungus-gamboge a 

 yellow resinous substance which corresponds in all its deter- 

 mined characters with the gamboge-yellow which is the 

 chief constituent of gamboge. It occurs especially in the 

 sporophore of Polyporus hispidus, chiefly deposited in the 

 membranes, but also as an excretion outside of the mem- 

 branes and in the cell-contents. For its microchemical recog- 

 nition Zopf uses a solution of ferric chloride, which colors 

 fungus-gamboge, as well as membranes containing it, olive- 

 green or blackish brown. It is also insoluble in water, but 

 readily soluble in alcohol and ether ; it is dissolved with a 

 red color by concentrated nitric or sulphuric acid, and is 

 precipitated from these solutions in yellow flocks on the 

 addition of water. 



ft. Retinic Acid from Thelephora sp. 



147. Zopf has prepared (V, 77) a retinic acid from various: 

 species of Thelephora, which occurs partly in the cell-con- 

 tents and is partly deposited in or on the walls. It is insol- 

 uble in cold or hot water, soluble in alcohol, ether, methyl 

 alcohol, petroleum-ether, chloroform, benzol, carbon bisul- 

 phide, and turpentine. It is dissolved with a bluish-red 

 color by concentrated sulphuric acid, and thrown down 

 again with a greenish-yellow color on the addition of much 

 water. 



y. Retinic Acid from Tra metes cinnabarina. 



148. The retinic acid prepared by Zopf (V, 88) from the 

 above-named fungus agrees fully with the previous one in 

 its behavior with solvents ; but is distinguished from it by 



