﻿IX, B, 4 Barber: The Pipette Method 311 



carry out more successfully certain special applications of the 

 technique to be described below. 



The three-movement pipette holder containing a pipette and 

 clamped in position on the microscope is illustrated in figs. 1, 2, 

 and 15, showing the front, that is, the side facing the observer, 

 the top, and the back, respectively. 



The adjustment ud, governed by the screw s, allows an up- 

 and-down movement. The adjustment rl, governed by the screw 

 s', allows a movement to the right or left, and the adjustment 

 tf and the screw s" (fig. 15) allow a movement to and from 

 the observer. The to-and-from movement carries the two other 

 adjustments with it, and the up-and-down adjustment carries 

 the in-and-out. The holder is fastened by the clamp cl to 

 the metal plate pa or pb, which is screwed to the stage of the 

 microscope. The pipette is held in the groove g (fig. 2) in the 

 side of the adjustment rl, and is fixed by the set screw ss, 

 which moves the thin plate tp. A two-movement holder is 

 shown in fig. 9 and in fig. 15, B. 



The small tightening screws on the holder should be so ad- 

 justed that the up-and-down movement can be easily manipulated 

 with one finger only. This will allow a rapid lowering of the 

 pipette. 



The holder may be clamped directly on the stage of the 

 microscope, but in most types of microscope the pipette is 

 brought to a more convenient level and more working room 

 allowed if a metal plate (see pb, p, and pa, figs. 1, 13, and 15) 

 is screwed on the bottom of the stage of the microscope. This 

 may be attached with thumb screws, so that it can be easily 

 taken off or put on. A convenient form is shown in p, fig. 13. 

 This type allows the holder to be set at either of two different 

 levels and at two different distances from the stage. In some 

 processes it is necessary to move the mechanical stage far to 

 the left. In this position the isolating chamber is apt to in- 

 terfere with the pipette holder, so it is well to have some arrange- 

 ment for clamping the holder 1 or 2 centimeters from the stage. 

 Either type p or type pa, fig. 13, will permit this movement. 

 Type pa may be attached when two holders are to be used or 

 when certain special processes are to be carried out. Another 

 form of plate is shown in pb (fig. 1). 



As a temporary expedient, the pipette holder may be attached 

 to a flat piece of wood placed under the stage. The wood is 

 shaped like the stage, perforated with an opening for the con- 

 denser, and provided with a shelf on the left for attaching the 



