Published online by Cambridge University Press: 15 May 2009
Futher experience with the method of measuring the precipitum obtained when experimenting with precipitating antisera has shown that finer degrees of reaction cannot be satisfactorily determined by means of the apparatus described by Nuttall. In the latter apparatus capillary tubes were used in which to measure the precipitum therein deposited. It is true that capillaries as far as possible of the same calibre were used, nevertheless we have found that different readings were obtained when experimenting with tubes of varying calibre, variations evidently due to physical causes which prevent an equal degree of “packing” of the deposit in tubes of unequal width. We have modified the method after finding that calibrated tubes of uniform bore gave more constant results, and have devised a simple apparatus which greatly facilitates the making of measurements.
page 201 note 1 Nuttall (5. iv. 1902), Brit. Med. Journ. vol. I, pp. 825—827, reprinted in Nuttall (1904), Blood Immunity and Blood Relationship etc. pp. 315—318.
page 201 note 2 A fine piece of glass rod, drawn out so that it tapers gradually, serves as a convenient cone for measuring the calibres of the tubing.
page 205 note 1 When, as sometimes happens, the precipitum does not settle entirely to the bottom, but becomes lodged in part in the upper portion of the tube, it can be made to sink by introducing a horse-hair which is twirled about and then withdrawn.