35 



CHAPTEK III 



NUTRIENT MATERIALS AND METHODS OF CULTIVATION 



Nutrient media. In order to observe the growth of 

 micro-organisms, it is absolutely necessary to provide 

 a number of nutrient materials in which the individual 

 microbes may multiply into larger masses, so that their 

 peculiarities can be more thoroughly made out. Some of 

 these culture media are so prepared as to approximate more 

 or less closely to the natural soil of the micro-organisms, and 

 others in such a manner as to render them suitable for use 

 as general media on which the most widely differing varieties 

 may be cultivated. They are divided generally into liquid 

 and solid media. 



Liquid nutrient media. Fluid media fall rather into the 

 background in use compared with the solid, since the con- 

 ditions of growth and characteristic pecu- 

 liarities in the shape of the colonies come 

 out less strongly on them than on the 

 latter. 



They are employed either in sterilised 

 test tubes closed with a plug of cotton- 

 wool, or in little flasks, of which those 



. -n , ,. , , f , , ERLEN-MEYEU'S FLASK. 



of Erlenmeyer are particularly useful (fig. 

 22). The media, especially bouillon or broth, after bein# 

 distributed into such smaller vessels, must be carefully 

 heated in the current of steam for 15 minutes daily on 

 three to five successive days, in order to sterilise them. The 



D 2 



