THK T} I'lIOID BACILLUS 279 



THE Hiss MEDIA: THEIR COMPOSITION AND PREPARATION/ Two 

 media are used: one for the isolation of the typhoid bacillus by plate 

 culture, and one for the differentiation of the typhoid bacillus from all 

 other forms in pure culture in tubes. 



The platiny medium is composed of 10 grams of agar, 25 grams of 

 gelatin, 5 grams of sodium chloride, 5 grams of Liebig's beef extract, 

 10 grams of glucose, and 1000 c.c. of water. When the agar is thor- 

 oughly melted the gelatin is added and completely dissolved by a few 

 minutes' boiling. The medium is then titrated, to determine its reac- 

 tion, phenolphthalein 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 normal acid. To clear the medium add one or two eggs, 

 well beaten in 25 c.c. of water, boil for forty-five minutes, and filter 

 through a thin filter of absorbent cot- 

 ton. 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 fit 

 grains; gelatin, 80 grams; sodium 

 chloride, 5 grams ; meat extract, 5 t ! 

 grams, and glucose, 10 grams to the 

 litre of water, and reacts 1.5 per cent, 

 acid by the indicator. The mode 

 of preparation is the same as for the 

 plate medium, care being taken always 

 to add the gelatin after the agar is 



thoroughlv melted, SO as not to alter HI plate media: Small light colony ) 

 , ! . . c ' , . , , ! , is composed of tvphoid bacilli ; large colony 



this ingredient by prolonged exposure (c) of colon baciiii. (From Hiss.) 



to high temperature. The glucose is 



added after clearing. The medium must contain 1.5 per cent, of 



normal acid. 



Growth of the Colonies. The growth of the typhoid bacilli in plates 

 made from the medium as above described gives rise to small colonies 

 with irregular outgrowth and fringing threads (Fig. 94). The colon 

 colonies, on the other hand, are much larger, and, as a rule, are 

 darker in color and do not form threads. The growth of the typhoid 

 bacilli in tubes produces uniform clouding at 37 C. within eighteen 

 hours. The colon cultures do not give the uniform clouding, and 

 present several appearances, probably dependent upon differences in 

 the degree of their motility and gas-producing properties in media. 

 Some of the varieties of the colon bacillus grow only locally where they 

 were inoculated by the platinum needle. Others grow diffusely through 

 the medium, but owing to the production of gas and the passage of 



1 This description is taken from an article by Dr. Philip Hanson Hiss, Jr., "On a Method of Iso- 

 lating and Identifying Bacillus Typhosus and Members of the Colon Group in Semisolid Culture 

 Media," published in the Journal of Experimental Medicine, 1897, vol. ii., No. 6. 



