379 
Dissection and Injection of Living Cells. 
a drop hanging from the roof of the chamber, the motion imparted 
by the mechanical stage moves the cells against the micro-needle. 
Indeed, most of the dissection, where a single needle is used, is 
done by first bringing the needle tip into the cell and then dragging 
the cell away by means of the mechanical stage. 
The horizontal movements of the micro-manipulator are used 
mostly for the purpose of bringing the tip of the needle accurately 
into a desired spot in the field of the microscope preparatory to the 
actual operative work. In order to ensure the greatest possible 
steadiness to the vertical movement, the part of the instrument 
which imparts this movement adjoins, and is manipulated from the 
stationary and rigid part of the instrument. To make this possible 
the present design incorporates a theoretical error which can be 
Fig. 3 1 . — Detail of brass collar (/ in fig. 3) which facilitates in 
and out movement of needle or pipette ; n, screw which presses on a 
spring to clamp the needle in the tube. 
Fig. 3 2 .— Detail of glass tube of injection apparatus -(l in fig. 3) 
cemented on brass tube j ; o, shank of micro-pipette sealed into 
end of glass tube. The pipette can be frequently changed. 
understood from fig. 1. Turning screw I, to produce the vertical 
movement, throws the combination of bars A, B and C out of the 
horizontal, and it is these bars upon which the lateral movements 
of the needle depend. However, the angle at which these bars are 
placed minimizes the error so as to be practically unnoticeable. 
Guides exist in the instrument to ensure a true travel of the 
bars as they spread apart or come together. The guide for the bar 
which produces the vertical movement consists of a depression in 
the stationary part of the instrument into which the vertical bar 
fits. The guides of the lateral movements are two metal discs 
which can be tightened or loosened by screws. The upper one is 
seen in fig. 2, /. They correct two possible errors which may occur 
on reversing the direction of movement, viz. a dropping of the 
needle or pipette out of focus and a shifting to one side. 
