﻿354 The Philippine Journal of Science. wu 



A clogged pipette may often be opened by gently scratching it 

 on the surface of the cover glass. Sometimes it is necessary to 

 enlarge the opening somewhat before it can be used. 



The cup must be well supplied with ice-cold water, and the hand 

 should be on the adjustment R, ready to bring it up quickly. 

 In case one is not particular as to the size of the dose, an excess 

 of bacteria may be drawn into the pipette and the pressure 

 stopped when some of the bacteria have come out. 



After the dose is in, the pressure is at once diminished and 

 the pipette withdrawn. With very fine tips the point may be 

 drawn out with little or no loss of cell contents. With larger 

 tips it is often necessary to withdraw the tip very slowly until 

 the plug of protoplasm, which usually forms at the point of 

 inoculation, is sufficiently firm to close the opening. In large 

 openings the dose is sometimes drawn back into the pipette on 

 reducing the pressure. Here one may introduce the tip just 

 through the layer of protoplasm and wait until a mound of 

 protoplasm has been formed over it before injecting. This will, 

 in many cases, act as a valve in closing the opening after the 

 dose passes out, so that the tip may be withdrawn safely. 



After inoculation, the cover may be removed and placed in a 

 moist chamber or sealed on a hollow slide. If it is desired to 

 keep the substance to be inoculated some distance from the 

 organism, it may be placed on another cover, the dose taken 

 in, the tip lowered, and the covers changed for inoculation. 



A filament grown beneath the surface of a hanging drop of 

 agar may be inoculated, but in that case it is well to have the 

 tip nearly at right angles with the capillary, else it may bend 

 too much in entering the agar. 



In working with pure cultures, it is sometimes necessary to 

 avoid getting any of the fluid or culture to be injected into the 

 medium outside of the filament. Here, after filling the pipette, 

 it may be quickly washed in a sterile hanging drop of water 

 or agar and then brought to the cell. It is obvious that a tip 

 with a relatively large opening may, if the pressure is negative, 

 draw in the washing fluid or air during transfer, or, if positive, 

 may eject prematurely part or all of the dose. So with such 

 points, it is best to have the pressure as nearly neutral as pos- 

 sible. Fine openings give much less trouble in this respect. 



If some bacteria are forced out into the surrounding medium, 

 it is sometimes possible to remove them with an ordinary pipette 

 attached to a rubber tube, such as is used in ordinary isolation. 

 These pipettes, either under or apart from the microscope, may 



