CHAPTER III.-METHODS OF DEMONSTRATING THE 



CHARACTER OF CELL-WALLS AND 



CELL-CONTENTS 



Aconitine,C33H4 3 NOi2. To demonstrate aconitine, treat sections with a solu- 

 tion of potassium iodide-iodine. If aconitine is present, a carmine-red color will 

 be produced. Treatment with a mixture of equal parts of sulphuric acid and water 

 gives a similar color. Treatment with a solution of cane-sugar and then with the 

 dilute sulphuric acid produces a brilliant carmine-red color. 



Aleurone. The protein nature of aleurone is shown by the fact that it dissolves 

 with a red color on the application of Millon's reagent, and assumes a yellowish 

 or brownish color with tincture of iodine. The aleurone grains of Ricinus are best 

 studied from material that has been fixed in a saturated alcoholic solution of picric 

 acid, or sections from fresh material may be fixed as above, rinsed in alcohol, stained 

 with an alcoholic solution of eosin, cleared in oil of cloves, and mounted in Canada 

 balsam. By this process the ground substance is stained red, the crystalloid yellow, 

 while the globoid is usually colorless. For characteristic reactions of aleurone 

 with other reagents, see in the last chapter under Borax-carmine, Digestive Fluids, 

 Gold Chloride, Pepsin. 



Alkaloids. Sections which are to be tested for alkaloids should be sufficiently 

 thick to leave one cell-layer intact. In order to make the determination of the 

 alkaloid more certain, sections for control should be soaked for a day or so in a 

 solvent of alkaloids prepared by dissolving i part of tartaric acid in 20 parts of 

 alcohol; and then the sections should be rinsed in water for a day to wash out the 

 acid solution. Sections which have been thus treated should be mounted under 

 the same cover-glass with untreated sections, and the reagents for testing for alka- 

 loids applied. It is best, on the whole, to mount the sections directly in the reagent 

 which is to be used as a test for the alkaloid, since some alkaloids might be dissolved 

 out if the sections are first mounted in water. 



With the following reagents most alkaloids are thrown down in the form of 

 amorphous or crystalline precipitates: Potassium iodide-iodine, potassium bis- 

 muthiodide, chlor-zinc-iodide, potassium-mercuriciodide, chloride of gold, am- 

 monium-molybdate. Phospho-molybdic acid, picric acid, chloride of platinum, 

 or a solution of bromin in hydrochloric acid. The crystalline precipitates can be 

 studied to best advantage by means of a polarizer attached to the microscope. 



The vapor of iodine may often be used to good advantage in the detection of 

 alkaloids in the following manner: A few grams of iodine are placed at the bottom 

 of a small exsiccator, and a layer of sand about a centimeter deep is placed over the 

 iodine to prevent its too rapid evaporation. Sections which have been treated 

 with a solvent of alkaloids, and sections which have not been thus treated, are 

 mounted on the same slide and placed on the upper part of the exsiccator, where 

 they are to remain for several hours. The sections are then covered with a drop 

 of paraffin oil, which will not dissolve the precipitate, and covered with a cover- 

 glass for examination under a microscope, preferably with a polarizing attachment. 



Allyl Sulphide, or Garlic Oil, (CsH 5 ) 2 S. This may be demonstrated by treating 

 portions of a species of Allium with a solution of palladous nitrate, which produces 

 with allyl sulphide a kermes-brown precipitate, or the material may be treated with 

 a 2 per cent, solution of silver nitrate, in which case sulphide of silver will be pro- 

 duced. The material may then be hardened in alcohol and sectioned. 



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