198 



An Apparatus for Liquid Measurement by Drops and Applications 

 in Counting Bacteria and other Cells and in Serology, etc. 

 By E. Donald B.Sc. (N.Z.), D.P.H. (Oxf.). 



(Communicated by Dr. L. Hill, F.R.S. Received November 21, 1912, — Read 



January 16, 1913.) 



(From the London Hospita Bacteriological Laboratory. Dr. William Bulloch, 



Director.) 



To promote drop-measuring in serological and bacteriological work, etc., 

 the writer has devised a simple system of producing uniform pipettes, clean 

 and sterile, which deliver uniform drops of any required size from £ c.c. down 

 to 1/200 c.c. or less, and has devised also simple forms of constant-pressure 

 apparatus for use with the pipettes. 



The fundamental principle of his method rests on the fact that the size of 

 a drop of a given liquid yielded by a clean pipette is determined by the outer 

 circumference of the pipette at the level where the contact-edge of the drop 

 clings round the glass — due allowance being made for the rate at which the 

 drop is detached and the temperature. 



The pipettes, freshly drawn out from glass tubing in a Bunsen flame to a 

 nearly cylindrical capillary form, are gauged in a wire gauge and cut off at the 

 required sizes. The gauges used are such as the Starrett Morse Drill and Wire 

 Gauge, which has holes ranging in diameter from 5*79 mm. down to 034 mm. 



Tubes larger than these sizes may conveniently be gauged by the Columbia 

 vernier slide gauge. Capillary tubes less than - 34 mm. may be gauged in a 

 wire drawplate. 



In gauging, the capillary tube is pushed gently down into the particular 

 gauge hole required and is then cut off — preferably at the upper surface of 

 the plate, so that the dropping-point shall not come into contact with any 

 trace of greasy matter which may remain on the cleaned gauge plate. 



To ascertain the size of drop yielded by such a dropping-point an adjustable 

 constant-pressure apparatus was devised. This (fig. 1) consists of a straight 

 tube of 3 to 4 mm. internal diameter and of such a length, e.g. 50 or 60 cm., 

 that the free air space within shall be amply greater than the capacity of 

 the pipette employed. The tube is carefully cleaned, washed finally with 

 distilled water, and dried with grease-free cotton wool drawn through on a 

 thread. The ends are opened out slightly funnel-shaped to facilitate the 

 ramming in of an inch or so of pure cotton wool, which is required to retard 



