LISTER'S FLASK— AITKEN'S TEST-TUBE. 



113 



aperture by tilting the flask to one side. On restoring the flask to its 

 upright position, it is found that though the liquid at once gravitates 

 back from the lateral bent tube, yet there is no regurgitation of the 

 mote-bearing air from without, which would almost inevitably con- 

 taminate the sterile liquid. This is prevented by a drop of liquid 

 that occupies the extreme end of the lateral tube, which it completely 

 occludes, and thus prevents the air from passing in. After a quantity 

 of the liquid has been withdrawn, a fresh sterile pad is placed over 

 the mouth of the lateral tube, and fastened in that position as above 

 described, and the residue of the stock liquid can be maintained 

 sterile for an indefinite period. 



Aitken's Test-Tube. 



63. This supplies a very convenient means of carrying on pure cul- 

 tivations in liquid media. The tube 

 (Fig. 58) has a lateral diverticulum 

 in the form of a narrow glass tube, 

 which tapers and ends in a fine im- 

 pervious point. The test-tube is 

 plugged with cotton wool, and 

 sterilised by superheating. It is 

 then charged with 10 c.c. of sterile 

 culture fluid, and incubated for four 

 or five days. If its contents remain 

 unaltered, it may be inoculated for 

 a cultivation experiment. To do 

 this the seed material is first pre- 

 pared on the tip of a sterile platinum 

 wire. The end of the lateral tube is 

 then snipped off" with a pair of sterile 

 (superheated) pliers, and the wire, 

 introduced carefully along the lateral 

 tube, deposits the seed material 

 upon the inner wall of the test-tube, 

 opposite to the point whence the 

 diverticulum springs. The wire is 

 then withdrawn, and the end of the 

 lateral tube sealed by fusing it in Fig. 58.— Aitken's Test-Tube. 



