Floatation technique

FLOATATION TECHNIQUE

Principle

  • The principle is to use an emulsifying fluid of a greater specific gravity than that of the parasite eggs, which result in flotation of eggs in the solution. Thereby mere examination of the solution in the top most layer will clearly indicate the presence of egg. The faecal material and fiber settle at the bottom.

Common floatation fluids/solutions

  • The common fluids in use are
    • Saturated solution of common salt (NaCl) of Sp.Gr.1.18-1.19
    • Saturated sugar/sucrose solution of Sp. Gr. 1.25
    • Saturated solution of sodium nitrate
    • Glycerine
    • Zinc sulphate solution (32.5 % solution) of Sp.Gr.1.18
    • A.E.X. (Acid HCl of Sp.Gr.1.03 + Ether + Xylol equal parts)
    • Magnesium sulphate

1. Lane's Method (Direct centrifugal floatation or D.C.F method)

  • A small quantity of the faeces is taken, emulsified in saturated sodium chloride solution or any other above mentioned solutions strained through a sieve and centrifuged. Examination of a few drops of the fluid from the topmost layer will reveal the eggs.

2. Willi’s technique (Leviation FLOATATION technique)

  • To faecal sediment made from centrifugal sedimentation technique add few ml of saturated common salt solution or any other floatation solutions and emulsify it.
  • Fill up to one third of a small floatation tube with a thick emulsion of the faeces and fill the tube to its capacity with the same solution.
  • Care should be taken to see that not a drop of the contents overflows.
  • Add one or two drops more of the solution till a convex surface is formed.
  • Allow it to stand for 10-15 minutes by which time all the eggs would have floated up.
  • Apply a clean coverslip or a slide to the surface of the fluid removing just that drop of the fluid containing the eggs, by means of capillary action.
  • This drop from the topmost layer is then examined under the low power of the microscope for eggs.

Advantages

  • Light infections are detected by this technique invariably.
  • Only eggs are clearly visible without the hindrance of faecal and fiber material.

Disadvantages

  • This method is useful in the examination of nematode infection only, since eggs of trematodes, most of the cestodes and even a few of the nematodes cannot be floated up. Different solution with different specific gravity is needed to float the eggs of different kinds of parasites.
  • The eggs may distort if kept in a floatation solution for long time.

Note

  • It is worthwhile to remember that almost all cestodes except the members of the Cotyloda do not discharge eggs, but segments containing numerous eggs are shed and passed out. Hence it is not always possible to find cestode eggs in samples.
  • A sizable quantity of the faeces is placed in a petri dish and with the aid of two mounted needles; the whole mass is searched for tapeworm segments which will be whitish in colour showing active movements while fresh.
Last modified: Tuesday, 17 April 2012, 7:39 AM