CULTURE MEDIA 75 



erine, etc. A very common modification is that of Wurtz, 

 where both lactose and litmus are added. 



Nonalbuminous (Synthesized) Media. The albuminous 

 media have a very indefinite composition, and it is quite 

 impossible to make two batches of media exactly alike. This 

 is very unfortunate because certain changes in the character- 

 istics of bacteria are caused by even slight changes in the 

 composition of the medium ; and it is sometimes difficult to 

 determine whether slight differences that are recognized in 

 cultures are due to inherent differences in the organism or to 

 differences in the culture media. It would be very desirable, 

 therefore, to have a culture medium of definite composition 

 which could be exactly reproduced from time to time. At- 

 tempts have been made to produce such media by the use of 

 chemically pure substances in which the nitrogen was fur- 

 nished in a comparatively low form, as, for instance, sodium 

 asparaginate. Dujardin showed that fungi could grow in 

 nonalbuminous substances as early as 1841. Later Pasteur 

 used them in his yeast work ; and in 1893 Uschinsky showed 

 that most pathogenic bacteria would grow on such media. 

 Uschinsky's medium, which may be given as an illustration 

 of these media, had the following composition : 



Water 1000 



Glycerine 30 to 40 



Sodium chloride 5 to 7 



Calcium chloride o.i 



Magnesium sulphate 0.2 to 0.4 



