LIQUID MEDIA. 93 



is gently warmed, and the extremity of the neck 

 nipped off with a pair of sterilised forceps. The 

 open extremity is plunged into the liquid contain- 

 ing the micro-organism, a minute quantity enters the 

 tube and mingles with the fluid in the bulb, without 

 fear of contamination by atmospheric germs. The 

 extremity of the neck is once more sealed up in the 

 flame of a Bunsen burner. 



Aitken's Tubes. These tubes are plugged and 

 sterilised, and the nutrient medium introduced as 

 into ordinary test-tubes. Instead of withdrawing the 

 cotton wool plug they are inoculated by means of 

 the lateral arm. The sealed extremity of the arm 

 is nipped off with sterilised forceps, and the in- 

 oculating needle is carefully introduced through 

 the opening thus made. It is directed along the 

 arm until it touches the opposite side of the test- 

 tube, where it deposits the material with which it 

 was charged. The needle is withdrawn, and the 

 end of the lateral arm again sealed up in the flame; 

 the test-tube is then tilted until the liquid touches 

 the deposited material ; on restoring the tube to 

 the vertical the material is washed down into the 

 body of the nutrient liquid. 



Pasteur's Apparatus. Special forms of 

 tubes, bulbs, and pipettes are employed by the 

 school of Pasteur. The tubes are provided with 

 lateral or with curved arms drawn out to a fine 

 point, and with slender necks plugged with cotton 

 wool. A double form shaped like a tuning fork, 



