﻿348 



The Philippine Journal of Science 



1914 



Fic. 17. Pipette for injecting sub- 

 stances into living cells. Com- 

 pleted. 



For convenience in description, the 

 curved portion will be designated as 

 the loop and the straight portion as 

 the arm. It is not essential to have 

 the exact form of loop as that rep- 

 resented in the figure. Sufficient 

 bends should be made to contain a 

 considerable quantity of mercury 

 and to make the instrument sen- 

 sitive to changes in temperature. 

 Too many bends make it heavy and 

 unwieldy. 



The tip n, drawn out into a coarse 

 capillary, is inserted into a cup of 

 mercury and the whole tube nearly 

 filled with mercury by exhausting 

 the air at the straight end. This 

 may be done conveniently by suction 

 through a rubber tube attached to 

 this end. The mercury should be 

 clean and dry ; it is best drawn into 

 the tube when hot. The tube should 

 be heated before filling, and all pre- 

 cautions should be taken to avoid 

 the introduction of bubbles of air 

 or of water vapor. After the tube 

 is filled to a point about 2 centi- 

 meters from the blunt end, the arm 

 should be inclined so as to leave the 

 capillary at n free from mercury. 

 Now constrict the capillary in the 

 flame at a point very close to the 

 loop until only a very fine lumen 

 remains. Raise the arm, and seal 

 the constricted portion just as the 

 outflowing mercury reaches it. By 

 this method very little, if any, air 

 remains at the tip. Loss of mer- 

 cury from the open end of the arm 

 may be avoided by temporarily plug- 

 ging the opening with cotton. 



Draw out the end of the arm into 

 a straight capillary about 8 centi- 

 meters long and 0.5 to 0.8 millimeter 



