Differentiation of Typhoid and Colon Bacilli 607 



red. If a glass rod dipped in hydrochloric acid be held over the dish, 

 vapor of ammonium chlorid is given off. The typhoid bacillus pro- 

 duces no acid in this medium, and there is consequently no change in 

 its color. Upon plates with colonies of both bacilli, the typhoid 

 colonies produce no change of color, while the colon colonies at once 

 redden the surrounding medium. 



Rothberger* first employed neutral red for the differentiation of the 

 typhoid and colon bacilli. When grown in fluid media containing it, 

 the colon bacillus produces a yellowish fluorescence, while the 

 typhoid bacillus does not destroy the port- wine color. Savage f and 

 Irons i have made use of the color reaction for the routine detection of 

 the colon bacillus in water. The best adaptation of the method is by 

 Stokes, who adds it to the various sugar bouillons in the propor- 

 tion of o.i gram per liter, and uses the medium in the fermentation 

 tube. The colon bacillus always ferments the sugars and produces a 

 typical color reaction. 



Hiss || recommends the use of two special media. 



The first consists of 5 grams of agar-agar, 80 grams of gelatin, 5 grams of Liebig's 

 beef-extract, 5 grams of sodium chlorid, and 10 grams of glucose to the liter. 

 The agar is dissolved in the 1000 cc. of water, to which have been added the beef- 

 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 reac- 

 tion indicating 1.5 per cent, of normal acid. To the clear medium add one or 

 two eggs, well beaten in 25 cc. 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 bacilhis 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-me- 

 dium, 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 tempera- 

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

 Of all the organisms upon which Hiss experimented with this medium, Bacilhis 

 typhosus alone displayed the power of producing thread- forming colonies. 



The colonies of the typhoid bacillus when deep in Hiss' 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 con- 

 sists 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 yel- 

 lowish-brown in color. Hiss claims that by the use of these media the typhoid 

 bacillus can readily be detected in typhoid stools. 



* "Centralbl. f. Bakt," 1893, P- 187. 



t "Journal of Hygiene," 1901, i, p. 437. 



j Ibid., 1902, n, p. 437. 



"Jour, of Infectious Diseases," 1904, i, p. 341. 



|| "Jour, of Experimental Medicine," Nov., 1897, vol. n, No. 6. 



