340 MEDICAL BACTERIOLOGY 



ty-four hours later the tube containing the largest amount of Pari- 

 etti 's solution which shows growth probably contains B. coli and B. 

 typhosus if it is present. The organisms may be separated most 

 quickly and easily by the use of the lactose litmus agar plate. The 

 blue colonies should be worked up, and especially tested for their 

 agglutinating power on typhoid blood. Instead of the lactose litmus 

 agar one of the following media may be used : 



B. Hiss' Plate Medium. ' This contains : 



10 grams of agar. 

 25 grams of gelatin. 

 5 grams of beef extract (Liebig). 

 5 grams of sodium chloride. 

 10 grams of dextrose. 

 1000 grams of water. 



It is made by first dissolving the agar, salt and extract in the 

 water, then the gelatin is added and dissolved, the reaction changed 

 by use of NaOH and phenolphthalein so that it will contain not less 

 than 2% normal acid, cleared with two eggs and filtered, dextrose 

 added and the medium tubed and sterilized. 



Make plate cultures in ordinary way and incubate at 38° C. for 

 18 hours, then examine the colonies microscopically. The colonies 

 of B. typhosus have irregular outgrowths and fringing threads. The 

 colonies of B. coli, on the other hand, are much larger and as a rule 

 are darker in color and do not form threads. 



The colonies may be further examined by the use of Hiss' Tube 



Medium. 



5 grams of agar-agar. 

 80 grams of gelatin. 

 5 grams of beef extract (Liebig). 

 5 grams sodium chloride.' 

 10 grams dextrose. 

 1000 grams water. 



Made as plate medium except that it is to contain 1.5% normal 

 acid. 



Within 18 hours at 38° C. the typhoid bacilli produce a uniform 

 clouding. The colon bacilli do not produce uniform clouding and 

 do produce gas. 



C. Medium op MacConket, as modified by Griinbaum.' 



•Jour. Exp. Med. 1897, 2: 677. 



« Brit. Med. Jour. 1902, Pt. 1, p. 1473. 



