SPECIAL CULTURE MEDIA 39 



SPECIAL CULTURE MEDIA. 



An enormous variety of different media has been brought 

 forward for use in cases either where special difficulty is ex- 

 perienced in getting an organism to grow, or where some special 

 growth characteristic is to be studied. It is impossible to do 

 more than give the chief of these. 



Peptone Solution. 



A simple solution of peptone (Witte) constitutes a suitable 

 culture medium for many bacteria. The peptone in the propor- 

 tion of 1 to 2 per cent., along with *5 per cent. NaCl, is dissolved 

 in distilled water by heating. The fluid is then filtered, placed 

 in tubes, and sterilised. The reaction is usually distinctly 

 alkaline, which condition is suitable for most purposes. For 

 special purposes the reaction may be standardised. In such a 

 solution the cholera vibrio grows with remarkable rapidity. It 

 is also much used for testing the formation of indol by bacteria ; 

 and by the addition of one of these sugars to it the fermentative 

 powers of an organism may be tested (p. 82). Litmus may be 

 added to show any change in reaction. 



Media containing an Indicator. 



Litmus Media. To any of the ordinary media litmus (French, 

 tournesol) may be added to show change in reaction during 

 bacterial growth. The litmus is added, before sterilisation, as 

 a strong watery solution (e.g., the Kubel-Tiemann solution, vide 

 p. 48) in sufficient quantity to give the medium a distinctly 

 bluish tint. During the development of an acid reaction the 

 colour changes to a pink, and may subsequently be dis- 

 charged. 



Neutral Red Media. This dye was introduced by Griinbaum 

 and Hume as an aid in determining the presence or absence of 

 members of the b. coli group, especially in the examination of 

 water. The media found most suitable are agar or bouillon con- 

 taining '5 per cent, of lactose, to which - 5 per cent, of a 1 per cent, 

 watery solution of neutral red is added. The alkaline medium 

 is of a yellowish brown colour which on the presence of acid 

 passes into a deep rose red. Sometimes there subsequently 

 occurs a change to a fluorescent green, caused apparently by a 

 change in the composition of the dye, as the fluorescence is not 

 discharged by addition of alkali. 



