BACILLUS TYPHOSUS. 431 



completely dissolved by a few minutes' boiling. The 

 medium is then titrated, to determine its reaction, 

 phenol phthalein being used as the indicator. The 

 requisite amount of normal hydrochloric acid or sodium 

 hydrate solution is added to bring it to the desired 

 reaction i. e., a reaction indicating 2 per cent, of nor- 

 mal acid. To clear the medium add one or two eggs, 

 well beaten it) 25 c.c. of water, boil for forty-five min- 

 utes, and filter through a thin filter of absorbent cotton. 

 Add the glucose after clearing. The reaction of the 

 medium is most important; it should never contain less 

 than 2 per cent, of normal acid. 



The tube medium contains agar, 5 grammes; gelatin, 

 80 grammes; sodium chloride, 5 grammes; meat ex- 



FIG. 54. 



Hiss' plate media: Small light colony (t) is composed of typhoid bacilli; 

 large colony (c) of colon bacilli. (From Hiss.) 



tract, 5 grammes, and glucose, 10 grammes to the litre 

 of water, and reacts to 1.5 per cent, acid by the indi- 

 cator. The mode of preparation is the same as for the 

 plate medium, care being taken always to add the 



