Differentiation of Typhoid and Colon Bacilli 651 



the addition of 2 per cent, of peptone, s per cent, of lactose, i per cent, of glucose, 

 0.5 per cent, of sodium sulphate, 2 per cent, of nitrate of potassium, and 3 per 

 cent, of a 2 per cent, solution of malachite green. 



In the medium the ordinary cocci and bacilli do not grow, Gart- 

 ner's bacillus and the paratyphoid bacillus b leave the medium clear, 

 but grow as a deposit at the bottom of the tube; the typhoid bacillus 

 destroys the green. If agar-agar be added, the colonies are sur- 

 rounded by a clear yellow zone. The colon and other organisms 

 grow slowly if at all. 



Not many workers were satisfied with the results obtained by 

 malachite green, nor were the results obtained uniform. A careful 

 study of the subject was made by Peabody and Pratt,* who found 

 great differences in the quality and reactions of different malachite 

 greens in the market. That with which Loffler worked was com- 

 mercially known as "120." They obtained three samples of this 

 dye, which varied in acidity between wide margins (0.2-1.0). 

 Experimenting with the different preparations, they found that the 

 least acid was the most useful preparation. The success of the 

 method, therefore, depends upon the adjustment of the concentra- 

 tion of the dye to the reaction of the medium. When this is done, 

 malachite green becomes a valuable adjunct to specific differentia- 

 tion. Their studies of the media led Peabody and Pratt to the inven- 

 tion of a new method of isolating typhoid bacilh from the feces. 

 Instead of employing malachite green agar-agar directly for this 

 purpose, they first employ malachite green bouillon as an "enrich- 

 ing" culture, and after eighteen to twenty-four hours' growth in the 

 incubator inoculate one or two large (20 cm. diameter) Drigalski- 

 Conradi plates, from which the colonies can subsequently be picked 

 out. 



Bile salts were first employed in culture-media by Limbourgf and 

 have been more or less popular ever since, though for differentiation 

 of typhoid and colon baciUi they cause occasional disappointment. 



Buxton and Coleman J prepare a medium composed of: 



Ox-bile '. . 900 cc. 



Glycerin 100 cc. 



Peptone 20 grams 



This was placed in a number of 100 cc. flasks, sterilized in the Arnold 

 sterihzer, and employed chiefly for blood-culture. ' The typhoid 

 bacillus grows well in it. 



Jackson§ prepares a medium for water examination when typhoid 

 and colon bacilli are suspected that consists of undiluted ox-bile; 

 if fresh ox-bile cannot be secured, an 11 per cent, solution of dry 



* "Zeitschrif t f. physiol. Chemie," 1889, iii, p. 196. 



t "Inst. hyg. Univers. Griefswald," see "Bull. Inst. Past.," iv. No. 9, May 

 IS, 1906, p. 393. 



I "Journal of Infectious Diseases," 1909, vi. No. 2, p. 194. 



§ "Biological Studies of the Pupils of W. T.- Sedgwick," 1906, University of 

 Chicago Press 



