ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



73 



Various methods of procedure are applicable. The most convenient 

 is that in which the pipette is manipulated by means of a special 

 holder, clamped directly on to the Microscope stage, or to a metal plate 

 fastened beneath. The best form of pipette-bolder possesses movements 

 in three directions of space as shown in rig. 6. The figure also shows 

 the other portions of the apparatus in position. The pipette is held in 

 a groove g in the side of the adjustment rl and is fixed by t),e set 

 screw ss. 



The moist chamber (fig. 7) is made by fastening strips of glass to a 

 slide with Canada balsam or any convenient cement, an additional strip 

 being cemented to the slide at the open end s, which serves to strengthen 

 the apparatus and makes it capable of holding water. A convenient 

 size for the moist chamber is 7»> mm. long, 35 wide, and 28 high. The 

 moist chamber is lined on the sides and end with filter paper, p, in order 

 to furnish a large moist surface. The cover glass, which should be of 

 a sufficient size to seal well over the sides of the chamber, needs .special 

 care in its preparation. • After careful cleaning, a little vaseline is 

 applied, the excess of vaseline is removed with soap and water, and the 



Fig. 7. — Isolating chamber, p, lining of blotting-paper ; 

 s, glass strip for retaining water in bottom. 



cover-glass, after warming, is rubbed with a dry clean cloth. The trace 

 of vaseline left behind is sufficient to prevent the hanging drops from 

 running together. Before use the cover-glass is sterilized, and a series 

 of drops of sterile broth are placed on the under side. 



The making of the capillary pipette presents some difficulties, and 

 experience is needed to obtain the best results. An ordinary capillary 

 pipette (0'5 mm. external diameter) is first drawn out in the Bunsen 

 flame. The shank of the pipette is held in the right hand, and with a 

 pair of fine forceps held in the left hand, the capillary is grasped at about 

 5 cm. from the shank, both hands resting on the table. The point of 

 the capillary next to the forceps is then held over the flame of a micro- 

 burner (fig. 8). When the glass begins to soften it is lifted slowly 

 from the flame and pulled so as to draw the capillary out into a very fine 

 point. The end of the capillary is then turned at right angles. The 

 pipette is placed in position in the pipette holder, and the tip brought 

 into view, and into the centre of the field of the Microscope by means of 

 the adjustments. The tip is then lowered. One of the drops of sterile 

 broth is then brought into the field, the objective is lowered until the 

 tip comes into view and the objective and tip are then raised together 

 until the tip comes into contact with the cover-glass just outside the 

 drop. The point of the capillary is then broken against the cover-glass, 



