(4) Glycerine.—Vide under methods of preservation of ova; to mount permanently, transfer to glycerine jelly; subsequently to harden the jelly, expose to formalin vapour.
Of these media, carbolic acid has the greatest refractive index excepting that of balsam. The latter may, in some cases, render structures too transparent, and it may be advisable to use only glycerine or glycerine jelly.
Preservation of Ova in Fæces, Urine, Bile, etc.
Heat some 70 per cent. alcohol in a basin to about 60 to 70° C. (until bubbles begin to appear). Add the fæces, etc., in the proportion of one part to about nine of fixative; keep stirring. Allow the sediment to settle. Transfer to a bottle with some fresh 70 per cent. alcohol.
Transference to Glycerine.—Prepare 5 per cent., 10 per cent., 20 per cent. solutions of glycerine in 70 per cent. alcohol. Pour off the alcohol in the bottle of fæces, etc., and replace by 5 per cent. glycerine solution. Allow to stand an hour or so. Then in the same way replace the 5 per cent. by a 10 per cent. glycerine, and finally by a 20 per cent. glycerine solution. When in this latter expose freely to the air (protecting from dust), so as to allow the alcohol and water to evaporate. Add a few drops of glycerine from time to time till eventually the ova are in pure glycerine. (In a very moist climate it may be necessary to use lime or calcium chloride to dry the air.) To mount permanently transfer some of the sediment to glycerine jelly.
Preservation and Examination of Cestodes.
Fixation.—(1) Saturated aqueous corrosive sublimate.—Add to this glacial acetic acid to the extent of 1 per cent. (Note this fixative will dissolve the “calcareous corpuscles”; 10 grammes of sublimate to 160 c.c. of water will give a saturated solution.) Warm the fixative to 70° to 80° C. (Avoid the use of needles.) Use plenty of fixative. Allow to act for a quarter of an hour or so. (a) Transfer to 70 per cent. alcohol. (It is advisable to remove the sublimate by the use of Lugol’s solution, or a solution containing tincture of iodine, adding this until the iodine colour is permanent.) Or (b) transfer for preservation to 10 per cent. formalin.
Or (2) 10 per cent. formalin.—In order to prevent contraction it is advisable to extend the tapeworm and keep it fixed by glass plates, or wind the worm around a wide glass tube or bottle, and then fix it.
Or (3) fix in hot alcohol.