Cultivation 543 



extract and sodium chlorid. When the agar is completely 

 melted, the gelatin is added and thoroughly dissolved by 

 a few minutes' boiling. The medium is then titrated to 

 determine its reaction, phenolphthalein being used as the 

 indicator, and enough HC1 or NaOH added to bring it to 

 the desired reaction i. e., a reaction indicating 1.5 per 

 cent, of normal acid. To the clear medium add one or two 

 eggs, well beaten in 25 c.c. of water; boil for forty-five 

 minutes, and filter through a thin layer of absorbent cotton. 

 Add the glucose after clearing. 



This medium is used in tubes, in which the culture is 

 planted by the ordinary puncture. The typhoid bacillus 

 alone has the power of uniformly clouding this medium without 

 showing streaks or gas-bubbles. 



The second medium is used for plating. It contains 10 

 grams of agar, 25 grams of gelatin, 5 grams of beef-extract, 

 5 grams of sodium chlorid, and 10 grams of glucose. The 

 method of preparation is the same as for the tube medium, 

 care always being taken to add the gelatin after the agar 

 is thoroughly melted, so as not to alter this ingredient by 

 prolonged exposure to high temperature. The preparation 

 should never contain less than 2 per cent, of normal acid. 

 Of all the organisms upon which Hiss experimented, with 

 this medium Bacillus typhosus alone displayed the power of 

 producing thread- forming colonies. 



The colonies of the typhoid bacillus when deep in Hiss's 

 medium appear small, generally spheric, with a rough, 

 irregular outline, and by transmitted light of a vitreous 

 greenish or yellowish-green color. The most characteristic 

 feature consists of well-defined filamentous outgrowths, 

 ranging from a single thread to a complete fringe about the 

 colony. The young colonies are, at times, composed solely 

 of threads. The fringing threads generally grow out nearly 

 at right angles to the periphery of the colony. 



The colonies of the colon bacillus appear, on the average, 

 larger than those of the typhoid bacillus; they are spheric 

 or of a whetstone form, and by transmitted light are darker, 

 more opaque, and less refractive than the typhoid colonies. 

 By reflected light they are pale yellow to the unaided eye. 



Surface colonies are large, round, irregularly spreading, 

 and are brown or yellowish-brown in color. Hiss claims 

 that by the use of these media the typhoid bacillus can 

 readily be detected in typhoid stools. 



