SPECIAL METHODS. 147 



glucin etc. after treatment with hydroxylamine, which 

 chemically unites with aldehydes, destroying the aldehyde 

 group (cf. Nickel II, 755). 



In what relation these aldehyde-like compounds stand to 

 the so-called lignin cannot at present be stated. 



257. For the microchemical recognition of lignification, 

 besides the behavior with cuprammonia and with iodine solu- 

 tion already described ( 251), the color-reactions given in the 

 foregoing table may be used. Of these reagents, aniline 

 sulphate and phloroglucin are especially good. The colors 

 produced by these substances last but a short time, while 

 thallin gives permanent colors and is therefore adapted to 

 the making of permanent preparations, which may be 

 mounted in glycerine-gelatine or in Canada balsam. 



258. Various pigments may also render good service in 

 the study of lignified walls. These behave quite differently 

 from un lignified walls with staining media and therefore cer- 

 tain staining solutions maybe well used for the distinction of 

 the different sorts of membranes. 



259. For the staining of lignified membranes fuchsin has 

 shown itself especially useful, and has already been recom- 

 mended by Van Tieghem and Berthold for this purpose. I 

 obtained very beautiful permanent preparations, in which 

 only the lignified walls were stained deep red, by leaving the 

 microtome sections first fora quarter of an hour or longer in 

 an aqueous solution of fuchsin, and then washing them for a 

 short time in a solution of picric acid, such as Altmann's, 

 which contains one part of a concentrated alcoholic solution 

 of picric acid to two parts of water (cf. 345). This makes 

 them dark-colored, and much of the color is then washed 

 out with alcohol ; finally they are passed into xylol anJ 

 xylol-Canada balsam. 



If a double staining is desired, it may be obtained by plac- 

 ing the sections, after the washing in alcohol, for an hour in 

 a suitable solution of haematoxylin, such as Bohmer's (cf. 

 315), aniline blue, methyl blue, or Berlin blue. After wash- 

 ing again in alcohol and mounting in Canada balsam, one 

 obtains preparations in which the lignified membranes are 



