MICRO-CHEMICAL REACTIONS. 



149 



Eosin gives a reddish coloration, and 

 the crystalloids remain yellowish if pic- 

 ric acid was used to fix. To bring out 

 the crystalloids we prefer to use acid 

 fuchsine. This stains the crystalloids 

 an intense red. Permanent preparation 

 should be preserved in balsam, glycerine 

 or some oil. 



Non-nitrogenous Contents, Of the non- 

 nitrogenous cell contents there are to be 

 considered, with a greater or less degree 

 of minuteness, oils, fats, starch, sugar, 

 amylodextrin and sulphur. 



The Fats and Oils can generally be de- 

 tected as small globules of a yellowish 

 or browmish color, circular or slightly 

 oval and of a high refractive index. 

 They are generally found lying free in 

 the cell cavities. In powdered drugs 

 they are dissociated and sometimes 

 run together in masses. Micro-chemi- 

 cally, osmic acid, 10 per cent., stains 

 them black; they are saponified by the 

 alkalies, a weak solution of KOH being 

 sufficient; tincture of alcanna stains fat 

 and oil globules bright red. Absolute al- 

 cohol distinguishes the fixed oils and fats 

 from the essential oils; the former are 

 insoluble, the latter soluble. A charac- 

 teristic reaction is seen when a section 

 of a plant to be investigated is placed 

 upon the slide in glycerine and slightly 

 warmed. The fats and fatty acids melt, 

 at first in drops, and then by slow cool- 

 ing crystallize in long needle-shaped crys- 

 tals collected in bundles. 



Starch is distinguished both morpho- 

 logically and micro-chemically with 

 great readiness. It makes a characteris- 

 tic reaction with iodine solution, varying 

 with the strength of the solution and the 

 length of application from blue to violet 

 to black; alkalies destroy the coloration 

 and acids restore it. 



The Constituents of the Cell Sap are 

 the most numerous of the cell contents, 

 and much research is necessary to dif- 

 ferentiate all the substances thus far de- 

 scribed; hence they can be hardly more 

 than touched upon. These materials in 

 solution include hesperidin, inulin, as- 

 puragin, tyrosin, aloin, sugar, mucilage, 

 tannins, alkaloids, glucosides, bitter 

 stuffs, ethereal oils, gums, resins, rub- 

 bers, milky juices, balsams, plant acids, 

 and various crystals. A number of 

 these are of little importance save in the 

 znost detailed investigations, while oth- 



ers are constantly determined by chem- 

 ical means, and their presence can fre- 

 quently be made evident by means of the 

 microscope. The more important con- 

 stituents from our present standpoint are 

 tannin, resins, sugar, wax, the alkaloids, 



and the glucosides. 



Sugar. Although Trommer's and Feh- 

 ling's tests are most often given for the 

 detection of sugar, it is not an easy mat- 

 ter to determine its presence in small 

 quantities; Phenylhydraziue acetate has 

 given satisfactory results in our experi- 

 ence when the amount of sugar has been 



very small. 

 Tannin is found extensively in plants, 



generally dissolved in the cell sap, espe- 

 cially of the bark; it is often found in 

 gianular form also. As a general micro- 

 chemical reagent for tannin, ferric chlo- 

 ride is used, either in aqueous or alco- 

 holic solutions. Ferric sulphate and ace- 

 tate give less intense reactions. If a 

 substance is impregnated with any of 

 these mixtures, the masses of tannin or 

 the cellulose membranes impregnated 

 with tannin give a bluish or greenish re- 

 action, strong solutions giving a blue- 

 black or greenish-black reaction. The 

 taimin in galls, oak for instance, give 

 the bluish reactions, whereas rhatauy, 

 coffee, and male fern give the greenish 

 reaction. Potassium bichromate is also 

 of value, giving after some time a red- 

 dish coloration, A dilute solution of 

 zinc chloride gives a reddish violet colo- 

 ration with tannin. 



Resins are found either fluid or in more 

 or less solid granules, sometimes lying 

 in the cell wall, sometimes in special se- 

 cretory reservoirs, or partly saturating 

 the cell walls. The resins are generally 

 brownish in color, and if in grains, ir- 

 regular in shape. Tincture of alcanna, 

 50 per cent., stains resin a cinnamon red. 

 A solution of equal parts methyl-violet, 

 fuchsia, and alcohol (Hanstein) produces 

 a blue, or clear green, or dirty green 



color. 



The Alkaloids and Glucosides, micro- 

 scopically, are more of a hope than a real- 

 ity in practical work, for in their natural 

 condition they are difficult if not impos- 

 sible to recognize. Micro-chemically, 

 however, much can be done in their de- 

 termination, but the work is for the ad- 

 vanced student rather than the tyro, and 

 to undertake it one should consult the 

 works already noted. 



