iv.] PREPARATION OF CULTURE-MEDIA. 



35 



I have opened under these conditions the plugs of test- 

 tubes containing sterile material, and kept them so for a 

 time varying from one to ten seconds, and in some in- 

 stances I have not seen more than from 10 to 20 per cent, 

 contaminated, often less. 



Now, having filled the required number of test-tubes and 

 flasks with the desired quantity of fluid, I subject these 

 seriatim to boiling. By means of an ordinary test-tube 



FIG. 8. A BEAKER CONTAINING A NUMBER OF CULTURE-TUBES PLUGGED 

 WITH COTTON-WOOL. 



holder I hold them above a very small flame until the fluid 

 boils, and keep it so boiling for from two to five minutes. 

 During this process of boiling the cotton-wool is only slightly 

 pulled up, and immediately before ceasing to boil the plug is 

 again replaced, aud pushed down with a clean glass rod. 

 Then the test-tube is placed (of course upright) in a beaker 

 at the bottom of which a layer of cotton-wool a sort of 



D 2 



