CHAPTER VII. 



THE PREPARATION OF MEDIA FOR THE CULTIVATION OF 



BACTERIA. 



Preparation of retainers. In order to study the proper- 

 ties characteristic of the different species of bacteria.it is 

 necessary to cultivate them under artificial conditions. The 

 successful cultivation of bacteria, especially the pathogenic 

 species, requires close adherence to several fundamental pro- 

 cedures. For the purpose of cultivation and the study of 

 the properties of the individual species and strains of bac- 

 teria, certain culture media are necessary and in their prepa- 

 ration certain preliminary work is necessary. 



Before using the test tubes and flasks for receiving the 

 media they must be thoroughly cleaned. It is also important 

 that they be sterile. The test tubes and flasks must be 

 plugged with cotton.* Absorbent cotton with a long fibre is 

 best adapted to this purpose. Common cotton can not be used 

 satisfactorily unless it is previously degreased. Test tubes 

 can ordinarily be cleaned by washing them with a strong 

 alkali soap and water, using the best tube brush. They must 

 be thoroughly rinsed, preferably in hot water, and drained. 

 Petri dishes and flasks must also be cleaned in this way. 



* It is important in opening and closing cultures for purposes of 

 examination to have tubes closed with well made plugs. For this 

 purpose absorbent cotton is used. Rolls of it are cut in short seg- 

 ments of from 5 to 7 cm. in length. A piece of this narrow strip of 

 sufficient length to give cotton enough for the plug is torn off. The 

 quantity varies, of course, with the size of the mouth of the tube or 

 flask, but a little experience will enable one to estimate the quantity 

 quite accurately. The edges of the piece of cotton torn off are 

 turned in and it is rolled up to form a firm plug which should snugly 

 fit the neck of the tube or flask. It should be inserted into the tube 

 for about 3 cm. and the end should be nearly flat and smooth. The 

 projecting part should be about the same ^ngth, of equal firmness 

 and project over the lip of the tube if it has one. 



