The titration of diphtheria toxin by the flocculation method / A.T. Glenny and U. Wallace.

  • Glenny, A. T.
Date:
[1925?]
Catalogue details

Licence: In copyright

Credit: The titration of diphtheria toxin by the flocculation method / A.T. Glenny and U. Wallace. Source: Wellcome Collection.

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    and 0'75 cm. in diameter, flocculated in 40 minutes and 47 minutes respectively under identical conditions when one - third immersed, and in 54 minutes and 74 minutes respectively when fully immersed. 2-0 c.c. and TO c.c. volumes of the same mixture in tubes of the same diameter flocculated in 42 minutes and 47 minutes side by side in the bath, the tubes being equally, and the columns of liquid unequally, immersed. If, however, uniformity of heating and of con¬ vection currents is ensured by totally immersing the tubes, the ■: volume of mixture, provided there is sufficient to give a visible : precipitate, does not appear to influence the rate of flocculation; : 5’0 c.c. and TO c.c. volumes of the same mixture, completely immersed, I both flocculated in 40 minutes; it is, however, difficult to ensure a si simultaneous rise of temperature in very unequal volumes of liquid in the same bath. It is essential to have all the tubes in one series uniform since mixtures in wide tubes flocculate more slowly than in narrow, and to have exactly the same volume of liquid in each tube since the depth of immersion affects the rate of flocculation. The thickness of the bottom of drawn out glass tubes varies considerably, so that unless the tubes are carefully selected the amount of liquid immersed will not be i equal in tubes immersed to the same depth, even though the diameter of the tubes is the same. Relation between time of flocculation and strength of fresh toxins. The number of conditions upon which the rate of flocculation j depends is so great that Tf., the flocculation time for a balanced 1 mixture, has only a relative value. The relative rates of flocculation j of different toxins can be compared if the toxins are titrated under identical conditions. A group of toxins, all prepared during a period of three months from the same strain but on a variety of media were i tested simultaneously on scale A, i.e. the antitoxic content of adjacent tubes differed by 5 per cent. The Lf and Tf. are plotted on chart 3 which shows, since the points all lie on a smooth curve, that the rate of flocculation of fresh toxins is a function of the strength of the toxin. The strongest toxin flocculates most rapidly, e.g. that containing 26 Lf units per c.c. flocculated in 8 minutes, while the weakest toxin ; in this series containing 6 Lf units per c.c. did not flocculate until: 75 minutes had elapsed. With such varying conditions as arise from day to day with routine tests the connection between Tf. and | strength is not so uniform. To evaluate any batch of toxin it is necessary for conditions to be constant in one series of mixtures but it is not necessary for them to be constant between different series. In j practice a test upon one toxin may have been made at a temperature; several degrees lower than that at which another toxin had been tested, j The temperature of the air above the bath differs markedly on different