MICROCHEMISTRY. 75 



Since wax is not wetted by water, the study of the various 

 rods, granules, etc., is better conducted in cold alcohol 

 which wets the wax without dissolving it at once, to say the 

 least. 



115. The waxy incrustations of suberized membranes, 

 observed especially on various epidermal cells, as, for ex- 

 ample, those of Aloe verrucosa, become at once visible, 

 according to DeBary (I), if the sections are warmed under 

 a cover-glass to near the boiling point of water. They then 

 separate from the membrane in the form of drops. These 

 drops are soluble in boiling alcohol and behave chemically 

 like the wax coverings described. Wax may also be ex- 

 tracted from the incrusted membranes by boiling alcohoL 

 The membranes always suffer in consequence a correspond- 

 ing reduction of volume, which cannot be made good by 

 subsequent immersion in water. 



5. Carbohydrates. 



116. The carbohydrates are characterized, as is well 

 known, by the fact that they contain, besides carbon, hy- 

 drogen and oxygen in the same proportion as in water, so 

 that their general formula may be written CxH2yOy. 



Of course not all organic compounds which show thisr- 

 empirical formula are included in the carbohydrates, and 

 already various substances which were formerly included 

 here have been transferred to other places in the natural 

 system of organic compounds, after their constitution has, 

 become more exactly known. And the recent investiga- 

 tions of Emil Fischer (I) have introduced a more rational 

 classification of the carbohydrates. 



But these investigations have at present no significance 

 for microchemical methods, since the certain microscopical 

 separation of the compounds of this group is as yet possible 

 only in very rare cases. I will therefore restrict myself 

 here to the description of microchemical methods for recog- 

 nizing some soluble carbohydrates. The solid carbohy- 

 drates, cellulose and its derivatives, as well as starch and 



