REAGENTS AND PROCESSES 545 



Dissolve the borax in water and add the carmine, which is quickly dissolved 

 with the aid of gentle heat. Add 100 mils of 70 per cent, alcohol and filter 

 (Stirling). 



Gum Arabic. -The study of the spermatozoids of ferns, etc., is facilitated by 

 adding a 10 per cent, solution of gum arabic to the drop of water containing 

 the spermatozoids, which are then unable to move so rapidly in the thicker fluid. 



Haematein. Dissolve with heat i Gm. of haematein in 50 mils of 90 per cent, 

 alcohol, and add to this a solution of 50 Gm. of alum in i liter of distilled water. 

 After cooling, filter if necessary, and add a crystal of thymol to prevent the growth 

 of fungi. The solution is ready for use at once. Sections stained in this solution 

 should be washed in water and transferred to glycerine-gelatine for mounting, or 

 may be dehydrated and mounted in Canada balsam. The stain may be reduced 

 in overstained sections by allowing the preparation to stand for some time in a I 

 per cent, solution of alum. A sediment is apt to settle from this solution, but this 

 is not an indication that the stain is spoiled. The sediment can be partly prevented 

 by adding to the solution about 2 per cent, of glacial acid, which, on the whole, 

 increases the effectiveness of the stain. The acid should be entirely washed from 

 the sections with water before permanent mounts are made. 



Hsematoxylin, Delafield's. Prepared by mixing 4 mils of a saturated solution 

 of haematoxylin crystals in absolute alcohol with 1 50 mils of a saturated solution of 

 crystals of ammonium alum in water. After standing for a week exposed to the 

 light, this should be filtered and mixed with 22 mils of glycerine and 25 mils of 

 methyl alcohol. Before using this it should be allowed to stand until all precipi- 

 tates have settled. 



Haematoxylin and Eosin. These may be combined to form a double stain by 

 adding the above solution to a mixture of equal parts of glycerine and a saturated 

 alcoholic or aqueous solution of eosin, until the green fluorescence of the eosin has 

 entirely disappeared. 



Haematoxylin and Safranin. Sections stained in safranin and washed in water 

 may be placed for a few minutes in a solution of o. i Gm. of alum in 30 mils of water 

 to which have been added a few drops of a solution of 3.5 Gm. of haematoxylin in 

 100 Gm. of alcohol. The haematoxylin and alum mixture should stand a few days 

 before using. By this treatment lignified and suberized walls are stained red and 

 cellulose walls violet. 



Hanging -drop Culture. A hanging-drop culture is useful in the study of various 

 microorganisms. A glass or vulcanite ring, obtained of the dealers for the purpose, 

 is cemented to the ordinary glass slip with Canada balsam or melted paraffin. A 

 round cover-glass, which should have a diameter at least as large as the. outside 

 diameter of the ring, should be thoroughly cleaned, and sterilized by baking in a 

 hot-air sterilizer. Then the slide may be held with sterilized forceps, or placed on 

 any convenient support, while a drop of nutrient substance is placed on the cover- 

 glass by means of a sterilized glass rod. By means of a sterilized platinum needle 

 a few individuals of the organisms to be studied may be transferred from pure 

 cultures to the drop of nutrient fluid on the slide. Then the cover-glass should be 

 quickly inverted over the ring cemented to the glass slip, the upper surface of the 

 ring having been previously lightly coated with vaseline, which serves to hold the 

 cover-glass in position and, at the same time, prevents the drop from evaporating. 

 If a single organism is desired in the hanging drop, a few of the organisms from a 

 pure culture may be transferred by means of a sterilized platinum needle to some 

 sterilized nutrient liquid in a test-tube; the tube should be twirled between the palms 

 of the hands to distribute the organisms, and then a drop from the test-tube should 



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