Dissection and Injection of Living Cells. 
383 
The thicker the wall of the tubing the firmer tends to be the tip 
of the needle made from it. The method of making the needle is 
given in a paper of Barber’s (1914), and in one of mine (1918). 
A brief account will suffice here. Acetylene or ordinary 
illuminating gas may be used. For a micro-burner use a piece of 
hard glass tubing bent at right angles, and with the burner end 
closed except for the smallest aperture that will retain a flame. 
This may be done by heating the end and pinching it with forceps. 
The size of the flame may be regulated by a screw pinch-cock on 
the rubber tube (fig. 5, h). 
To make the needles proceed as follows : — 1. In an ordinary 
burner draw out one end of a glass tube with a capillary of about 
0.3 — 0.5 mm. in diameter (fig. 5, a). 2. Lower the flame of the 
micro-burner to the smallest flame possible. Now hold the shank 
of the tube in the left hand and grasp the capillary at its end 
either with the thumb and finger of the right hand, or with forceps 
having flat tips coated with Canada balsam. Bring the capillary 
over the flame and pull gently till the capillary parts. The 
hands should remain on the table during the process, and, as the 
capillary parts, lift the glass away from the flame by turning the 
hands slightly outward. The capillary will separate with a slight 
tug. The tip should be like that in c. If too little heat is used 
and the pull made too suddenly, the capillary may part with a 
snap with a broken tip. If too much heat is used the tip is 
drawn out into a long hair, e. 3. Bend the capillary at right 
angles by heating it just back of the point and pushing up with a 
dissecting needle, b. The length of the needle beyond the bend is 
conditioned by the height of the moist chamber to be used. The 
type of needle shown in g is used for cutting by bringing the 
upper limb of the needle below and up into the cell. 
5. Apparatus for Injection and for the Withdrawal 
of Material from a Liyinq Cell. 
Barber’s mercury pipette method, which depends upon the 
expansion and contraction of mercury by heat and cold, although 
excellent, is troublesome to make and easily broken. Taylor 
(1920) devised an instrument which depends upon a plunger to 
exert pressure on an enclosed mercury column. With mercury, 
however, it is difficult to maintain a plunger for any length of 
time without leakage. 1 described an apparatus (1921) in which 
mercury or nujol oil is enclosed in a thin-walled steel cylinder. 
Pressure on the wall of the cylinder exerts the driving force 
necessary for injection. This works very well, but it requires 
special apparatus, and the difficulty of securing a cylinder the 
walls of which are sufficiently resilient renders the apparatus 
somewhat unserviceable. 
