CULTIVATION OF BACTERIA. 



189 



need not be sterilized before using, as the culture-medium 

 will be sterilized by the intermittent method after the 

 tubes are rilled. The test-tubes and flasks into which 

 the culture-medium is filled must, however, be previously 

 sterilized by dry heat. The dry-heat sterilization is done, 

 of course, after the cotton plugs are in place. 



Bouillon is the basis of most of the culture-media. 

 The addition of 10 per cent, of gelatin makes it "gela- 

 tin ;" that of 1 per cent, of agar-agar makes it "agar- 



Fig. 21. — Funnel for filling tubes with culture-media (Warren): a, funnel 

 containing the culture-media in liquid condition ; b, pinch-cock by which the 

 flow of fluid into the test-tube is regulated ; c, rubber tubing. 



agar." The preparation of these media, however, varies 

 somewhat from that of plain bouillon. 



Sugar Bouillon is bouillon containing in solution 

 known percentages of such sugars as glucose, lactose, 



