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The Philippine Journal of Science 



19U 



and lowering of the cup containing cold water may be done 

 by an assistant. I have successfully inoculated defibrinated 

 human blood into living mosquitoes by this method. 



A special application of the pipette may deserve a fuller de- 

 scription. In this technique the separation of motile bacteria is 

 accomplished by the use of pipettes supplied with fluids attrac- 

 tive or repulsive to certain species of bacteria. For certain 



experiments specific agglutinat- 

 ing serums may also be used. A 

 short glass tube is plugged at 

 one end with cotton and drawn 

 out into a capillary at the other. 

 It is then sterilized in the hot- 

 air sterilizer. An ordinary pip- 

 ette is made from it, supplied 

 with the fluid to be used, and is 

 placed in a test tube or flask con- 

 taining the mixture of bacteria, 

 as shown in fig. 16. A perfor- 

 ated cork may be used in place 

 of the cotton plug, and, in either 

 case, two or more pipettes may 

 be introduced into the same 

 flask. The pipette is supplied 

 with liquid from a test tube and 

 more drawn in than can be sup- 

 ported by capillarity. The liquid 

 flows out of the capillary until 

 only the column supported by 

 capillarity remains. The slow 

 diffusion of the liquid from the 

 point forms a zone of attraction 

 for motile bacteria positively 

 chemotactic to the fluid in the 

 pipette, and they may finally 

 enter the pipette and grow in 

 the capillary. It is easy to transfer them by removing the 

 cotton plug from the pipette and withdrawing some of the liquid 

 at the top of the column by means of a fine glass capillary or a 

 long platinum needle. If it is desired to continue the use of the 

 apparatus after the removal of liquid for examination, the pip- 

 ette may be raised slightly after withdrawal of the liquid, so 

 that no additional bacteria will be drawn into the tip by capil- 

 larity, or new liquid may be introduced into the capillary. 



Fig. 16. Apparatus for attracting certain 

 motile bacteria into pipettes. 



