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A MANUAL OF BACTERIOLOGY 



0-05 c.c. Finer pipettes 0-1 c.c. divided into tenths- 

 can be obtained by which approximately 0-01 c.c. may 

 be delivered. 



For the measurement of quantities less than 0-1 c.c., 

 however, the most practicable and accurate method is 

 the drop method elaborated by Donald. 1 While the 

 method is more suitable for arbitrary volumes it may also 



be used for definite measured volumes. The volume of a 

 drop depends upon three principal factors : the external 

 diameter of the dropping point, the surface tension of 

 the liquid, and the temperature of the liquid : if measure- 

 ments are done at room temperature, the last-named may 

 be neglected. Pipettes drawn out of glass tubing are 

 employed, similar to those used for opsonic determina- 

 tions (Fig. 36, a, p. 260). A pipette is calibrated by gently 

 pushing it into the suitable hole of a wire gauge until 



1 Lancet. 1915. vol. ii. p. 1243. and 1916, vol. ii, p. 423. 



