18 GENERAL TECHNIC 



If the latter must be sealed, as when working aseptically, rubber stoppers 

 should be used. However, if cotton plugs are large and fit tightly, 

 they may be prevented from becoming displaced by passing through 

 them two cross-pins in such manner that the ends will rest upon the 

 edge of the tube. The plugs are thus prevented from being thrown to 

 the bottom of the tube. 



FIG. 1. ELECTRIC CENTRIFUGE. 

 Mounted on a concrete s ge fcrtja purpose of W ei g hin g and 



7. If the centrifuge is out of order, however slightly, it should not 

 be used, but repaired at once, or else it may be ruined. 



PIPETS 



1. Simple Capillary Pipets.-These are made of soft glass tubing 

 in the following way : 



