40 PRACTICAL BACTERIOLOGY. 



sterilisation with dry heat ; it is especially useful for 

 killing bacteria on instruments and in apparatus, 

 vvhicli are not injured by being subjected to great heat 

 for a long time. 



The blood serum is taken up with a pipette, which 

 has been sterilised in a similar manner, and is poured 

 into these sterilised test-tubes, until they are a third- 

 part full. The cotton-wool plugs are then immedi- 

 ately replaced. The best method of manipulation is 

 as follows : — The cot,ton-wool plug is held between the 

 third and fourth fingers of the right hand, whilst the 

 empty test-tube is held in the left. The sterilised 

 pipette is held by its upper end between the thumb 

 and middle finger of the right hand ; the blood serum 

 is sucked up, and the upper opening is stopped up 

 with the index finger. The fluid is now allowed to flow 

 into the empty test-tube, after which the latter is 

 immediately closed with the cotton- wool plug. The 

 test-tube is then replaced, a second one is taken with 

 the left hand, the stopper withdrawn as described 

 above, etc., until they are all filled. A word of cau- 

 tion is necessary. The greatest possible care must be 

 taken not to touch any unsterilised object with the 

 pipette whilst the test-tubes are being changed, nor to 

 lay it down, as otherwise there is considerable danger 

 of introducing bacteria into the serum, and thus 

 rendering it useless. The same is true of the cotton- 

 wool stopper, which is held whilst the test-tube is being 



