Hints from the Health Department. Leaflet from the archive of the Society of Medical Officers of Health. Credit: Wellcome Collection, London
[Report of the Medical Officer of Health for London County Council]
1. Suppose the titre of a serum is 60, and a solution with 3 doses per
volume is required. Find the dilution factor, f.
2. Suppose the same serum to be diluted 50 times. Find the doses of
complement in one volume of the solution.
Answer : d
= 1.2 dose per volume.
Table 1 has been prepared to facilitate the full appreciation of the detailed
discussion of the titration, and to show quantitatively why laking occurs most
rapidly in the tubes with most complement, and slows down as the titre strength at
30 minutes is approached, until finally it ceases in the tubes with less than one dose
of complement. These latter tubes, therefore, show partial laking of the red cells,
ranging from almost complete lysis to only a faint trace (if any) with the weakest
|Doses of comp. per vol of guinea-pig serum Titre.||Tubes with one volume of diluted guinea-pig serum. (Numbers indicate tubes and also dilution factors.)|
|Doses of complement per tube.|
|N.B.—Underlined tubes show partial lysis, becoming less, since complete lysis can only occur when the minimum haemolytic dose (by definition above) or more is present.|
When setting up the tubes for the titration the rack is marked in tens, thus:—
20, 30, 40, etc., to indicate the dilution factors for each column of tubes, and the
tubes in the table are similarly indicated. The titres are read in multiples of three
because of the use of 3 M.H.D. of complement in the diagnostic tubes of the test,
and so it is convenient to have the titre number divisible by three.
Table I shows only a few possible titres for different specimens of guinea-pig
serum, but a full table can be similarly prepared to include all titres usually obtained,
ranging from 33 to 99. Such a table will show that, for each of the seven dilutions
from 40 to 100, there is a range of three or four titre-values within which the amount
of complement per volume varies from 1 dose to 1.15 dose as a maximum.
For any particular dilution of a serum (say, diluted 60 times), laking would be
complete within the range, but it would be no more than complete at the lowest titrevalue,
which is therefore (by definition) the true titre for the serum. This is shown
in table I by the unit dose being placed opposite and under the same figure for the
titre as for the dilution factor. Opposite the higher titre-values of the range for
the same dilution, more than a unit dose of complement is shown, and in such cases