Dissection and Injection of Living Cells. 385 
thin- walled capillary glass tubing. When finished the shaft of the 
needle should be at least 1J in. long and large enough to fit snugly 
into the glass capillary of the apparatus. This can be readily done 
by drawing out a supply of thin-walled glass capillaries and 
preserving those which fit a sample the size of the capillary of the 
apparatus. The needle end of the shaft should be bent at an angle 
the length from the knee of the bend to the tip, depending upon 
the height of the moist chamber. The shaft of the needle near its 
end is now thinly coated with de Khotinsky cement or sealing-wax, 
and, while the cement is still soft, inserted into the glass tube of 
the apparatus. An extra coat of cement should be added over the 
joint to ensure the seal. The apparatus is now ready for use. The 
tip of the needle is brought into a hanging drop of water or a 
solution, to be injected and converted into a pipette by jamming 
the tip against the under- surface of the coverslip until it breaks 
off.* During the process continual pressure should be exerted on 
the plunger of the syringe in order to prevent pieces of glass from 
being sucked into the pipette. Occasionally, while attempting to 
make the needle in the flame a serviceable pipette results instead. 
When the pipette is finally in place all or most of the air in it 
should be driven out. 
One can readily see that the sealing of the micro-pipette into 
the apparatus must be done away from the microscope. It is in 
this operation that the type of micro-manipulator fastened on a 
pillar is of advantage. The pipette has to be frequently changed, 
and it is very convenient to be able to release the microscope from 
its base by loosening its clamps and to slip it out of the way. As 
soon as a fresh needle has been inserted the microscope is readily 
slid back into place. For this purpose the base on which the 
microscope rests is provided with guides to ensure its true return. 
When exchanging a pipette care must be taken not to clog the 
lumen. This can be done by using a minimum amount of cement, 
and by having the lumen of the tube into which the shaft of the 
pipette is to be inserted as clean as possible. 
The use of thin-walled tubing for making the micro-pipette is 
to ensure having the largest bore possible at the tip of the pipette. 
The thickness of the wall and the size of the lumen of the glass 
tube tend to maintain their original proportions when drawn out 
in a flame. Often, however, it is more convenient to have pipettes 
with stouter walls. Such pipettes are less readily broken, but, 
owing to the smaller sized lumen, run the risk of quickly clogging. 
The best pipettes are made from hollow needles with a rapidly 
* For placing a hanging drop after the moist chamber has been covered, a 
convenient pipette is one with its end drawn out into a curved capillary and the 
tip bent at such an angle so that, on insertion into the moist chamber, the tip 
will touch the under-surface of the coverslip. With a rubber tube to reach one’s 
mouth a small drop is readily deposited. 
