BARBER: HEREDITY IN CERTAIN MICRO-ORGANISMS. 43 



Fig. 3. 



cross-lines, x, on the cover are in the center of the field. The 

 pipette is then adjusted by moving it in or out in the groove 

 at the side of g, or laterally by turning the screw, s, which 

 moves parts r and g of the holder. Adjustment is continued 

 until the pipette point is nearly in the center of the field of 

 the microscope. If higher powers are to be used, I usually 

 adjust the pipette under the two-thirds objective first, finally 

 placing it so that its tip is in focus near the center of the field 

 to be used. Finer adjustments may be accomplished laterally 

 by means of screw, s, and in the other direction by a slight 

 movement of the nose-piece holding the objectives. The 

 pipette, together with the parts g, k, and n, holding it, is 

 raised or lowered by means of an adjustment screw,/. The 

 part V is immovable, and remains clamped to the stage of the 

 microscope. 



When the pipette is in position it is fixed by the set-screw, 

 n, which tightens clamp k. By means of the mechanical 

 stage that portion of the cover bearing the sterile drop of 

 medium is now brought into the field, the tip of the pipette 

 raised into it and held until it partially fills, or the pipette 

 may be filled before it is placed in the holder by touching its 

 tip to a drop of nutrient fluid held in a sterile platinum loop. 



