540 POWDERED DRUGS 



then sections, not too thin, of the material which is to be tested for glucose are placed 

 in the mixture on the slide. It is best to cut the sections without wetting the razor, 

 and the sections should not be placed in water, but should be transferred directly to 

 the mixture on the slide. The sections should be covered with a cover-glass and 

 the slide carefully heated over the flame of an alcohol lamp, or a very small flame 

 from a Bunsen burner, until bubbles arise in the solution. If glucose is present, the 

 sections will appear reddish from very small crystals of cuprous oxide which have 

 been reduced from the solution. If it is not desired to observe the crystals of cuprous 

 oxide within the cells, but simply to demonstrate the presence of grape-sugar, small 

 pieces of the tissues to be tested may be placed in a test-tube containing a few mils 

 of the solution, which is then heated to boiling; if grape-sugar is present in con- 

 siderable quantity, a copious precipitate will after a time settle to the bottom of 

 the tube. See under Copper Acetate. This is particularly suitable for demon- 

 strating the presence of grape-sugar in those cells which contained it in the 

 uninjured tissues. 



Ferric-ammonium Sulphate. Used as a mordant. See under Double Staining. 



Ferric Chloride. An aqueous solution is used as a test for tannin. When sec- 

 tions containing tannin are placed in this solution on the slide, a color is produced 

 which may vary from dark blue to green. 



Ferricyanide of Potassium. Used in demonstrating the structure of pyrenoids. 

 Algae containing pyrenoids are placed in a mixture of equal parts of a 10 per cent, 

 solution of ferrocyanide of potassium and a 55 per cent, solution of glacial acetic 

 acid. Then, after staining with Hofmann's violet and swelling in dilute potassium 

 hydrate, the lamellated structure of the pyrenoids and the included hollow sphere 

 of starch-grains can be distinguished. 



Ferrocyanide of Potassium. A mixture of this salt and hydrochloric acid 

 diluted with 8 to 10 volumes of water is used to stain the nucleus of starch-bearing 

 Characeae. The starch is changed to sugar, by the hydrochloric acid, and Berlin 

 blue is produced, which is taken up by the nucleus, and, after clearing with chloral 

 hydrate, the nucleus becomes plainly visible. See also under Berlin Blue. 



Fischer's Method of Demonstrating Cilia. The following method is highly 

 recommended for demonstrating cilia of certain bacteria: An exceedingly small 

 amount of the culture containing the bacteria is spread out as thinly as possible 

 on the cover-glass. After the film has dried on the cover-glass the latter is passed 

 through the flame of an alcohol lamp or Bunsen burner (care being taken to avoid 

 a too excessive heat), and then a few drops of a mordant are put on the film on the 

 cover-glass. The mordant is prepared by dissolving 2 Gm. of tannin in 20 mils 

 of water. The cover-glass is then passed back and forth over a small flame until 

 vapor arises from the mordant. The mordant is now washed off by means of water 

 from a wash-bottle, and then one edge of the cover-glass is held in contact with a 

 piece of filter paper to draw away the surplus water. Next, a concentrated aque- 

 ous solution of fuchsin is spread over the film on the cover-glass, and the cover- 

 glass is held over a flame until the fuchsin solution begins to boil; the cover-glass 

 is then washed off, and is allowed to dry. At any time thereafter the cover-glass, 

 with the film side down, may be cemented to the slide with balsam. In success- 

 ful preparations made by this method cilia, when present, will stand out quite 

 sharply. 



Fixatives. All embryonic plant tissues, and those tissues, whether embryonic 

 or mature, whose protoplasmic cell-contents are to be studied, should be first fixed 

 and hardened preparatory to cutting thin sections from them. The object of fixing 

 is to coagulate the protoplasmic structures in the form which they possessed during 

 life. Subsequent dehydration and hardening prepare the material for imbedding 

 and sectioning. 



All the constituents of a fixative should penetrate the tissues quickly and at the 



