48 METHODS OF CULTIVATION OF BACTERIA 



organisms needing an abundant supply of oxygen the best 

 growth, takes place on the surface of the medium, and for 

 practical purposes the surface ought thus to be as large as 

 possible. To this end " sloped " agar and gelatin tubes are 

 used. To prepare these, tubes are filled only about one-sixth 

 full, and after sterilisation are allowed to solidify, lying on their 

 sides with their necks supported so that the contents extend 3 





Fro. 13. Tubes of media. 



a. Ordinary upright tube. b. Sloped tube, 

 c. " Deep " tube for cultures of anaerobes. 



FIG. 12. Apparatus which 

 may be used for filling tubes. 

 The apparatus explains itself. 

 The india-rubber stopper with 

 its tubes ought to be sterilised 

 before use. 



to 4 inches up, giving an oblique surface after solidification. 

 Thus agar is commonly used in such tubes (less frequently 

 gelatin is also " sloped "), and this is the position in which blood 

 serum is inspissated. Tubes, especially those of the less commonly 

 used media, should be placed in large jars provided with stoppers, 

 otherwise the contents are apt to evaporate. A tube of medium 

 which has been inoculated with a bacterium, and on which 

 growth has taken place, is called a " culture." A " pure culture " 

 is one in which only one organism is present. The methods of 



