Dissection and Injection of Living Cells. 
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the tip of the needle must be at the apex D of a right-angled 
isosceles triangle, the base of which is a straight line joining the 
centres, E and F, of the two springs holding the three bars A, B 
and C together. The shank of screw G passes through a large 
hole in bar C, and is screw-threaded in bar B. Turning if spreads 
apart bars A and B, and imparts an arc movement to the needle 
tip at I) at right angles to that procured by turning screw H. 
The movement in the vertical plane at right angles to the 
aforementioned movements is produced by screw I (fig. la), 
which is screw-threaded in a rigid vertical bar J, and abuts against 
a vertical extension K of bar C. The extension K is parallel to 
the bar J, and is connected to it at its top by means of a solid 
Fig. 1. — Diagram showing the working principle of the micro- 
manipulator. In la, where the instrument is viewed from the side, 
screw I moves needle tip through vertical arc y — z. In 16, where 
the instrument is viewed from above, screws G and H move the 
needle tip through the horizontal arcs m-n and o-p. 
spring hinge. Turning screw I spreads apart bars J and K, and 
lifts the whole combination (A, B and C) and imparts an arc 
movement in the vertical plane to the tip of the needle at D. To 
procure a vertical movement the tip of the needle at D must lie 
in the same horizontal plane L to D, with the spring fastening K 
and J together. When screw I is turned the needle tip will then 
move in an arc y to x , more nearly vertical than any other arc on 
the same circumference of which the point D is the centre. 
There are two models of the micro-manipulator. One is fitted 
with a clamping device with which it can be fastened directly to 
the front of the microscope stage (fig. 2, cf. fig. 3e). The other is 
fastened to a rigid pillar rising from a large metal base on which 
the microscope is clamped (fig. 2>a). The horizontal bars of the 
2 c 2 
