624 A MANUAL OF BACTERIOLOGY 



size (Fig. 56, c) must be provided to hold the quill tubes ; they 

 should have two or three rows of holes, numbered in sequence. 



A water-bath is used for standardisations and the test. The one 

 used by the author was made by Messrs. Hearson ; it is in copper, 

 and measures 13 in. long, 6 in. wide, and 4 in. deep (Fig. 56, a). 

 It is heated electrically, controlled by a regulator, and contains 

 two removable trays for tubes. Each tray has a back row of 

 twelve holes, 10 mm. in diameter, and a middle and a front row 

 of twelve holes each ; these holes measure about 7 mm. in 

 diameter, and hold the " quill " tubes. Other trays with holes 

 of any size may be substituted and the bath used for a " large 

 volume " technique. The holes are numbered in sequence. 



For standardisations and for the test the author uses five 

 throttled pipettes (Fig. 8, p. 60), which may conveniently stand 

 in short and long test-tubes in a test-tube rack (see Fig. 56, e). 

 These throttled pipettes are as follows : 



(a) One with a long (about 4|-5 in.) stem graduated into fifteen 

 unit volumes, and with a fine throttle. It is not necessary to 

 mark all the unit volumes, but it should be marked at 1, 2, ... 8, 

 and 14 and 15 unit volumes from the point upwards. If long 

 enough, it may be marked at 16 and 17 unit volumes in addition. 



(b) One with a longish stem (about 3| in.) graduated into 6 or 7 

 unit volumes, and with a fairly fine throttle. 



(c) One with a short stem (about 2|in.) graduated into 3 or 4 

 unit volumes and with a fine throttle. 



The unit volumes on the stems of these three pipettes should 

 measure | f in. in length. 



(d) One with a shortish stem (about 3 in.) and coarse bore 

 graduated at 5 and at 10 unit volumes. For convenience the 

 portion of the stem between the 5 and the 10 unit marks may be 

 slightly bulbous. The throttle need not be very fine. 



(e) One with a shortish stem (2|-3in.) graduated at 5 unit 

 volumes only, and with a coarse throttle. The pipettes are made 

 from glass tubing about f in. external diameter with not too thin 

 a wall. The pipettes are calibrated with the globule of mercury 

 obtained by measuring out 20 cub. mm. of clean mercury with 

 the hsemoglobinometer pipette. This volume of mercury is dis- 

 charged into a clean watch-glass and the globule is tipped into the 

 wide end of the pipette before the throttle is inserted and the 

 pipette is graduated by tilting the globule to and fro and marking 



