Cultivation 547 



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

 Gartner's bacillus and the paratyphoid bacillus 6 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 surrounded 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 reac- 

 tions of different malachite greens in the market. That with 

 which LofHer worked was commercially 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 

 concentration of the dye to the reaction of the medium. 

 When this is done, malachite green becomes a valuable 

 adjunct to specific differentiation. Their studies of the 

 media led Peabody and Pratt to the invention of a new 

 method of isolating typhoid bacilli from the feces. Instead 

 of employing malachite green agar-agar directly for this 

 purpose, they first employ malachite green bouillon as an 

 " enriching" 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. 



Gelatin Punctures. When transferred to gelatin punc- 

 ture cultures, the typhoid bacilli develop along the entire 

 track of the wire, with the formation of minute confluent, 

 spheric colonies. A small, thin, whitish layer develops 

 upon the surface near the center. The gelatin is not lique- 

 fied, but is sometimes slightly clouded in the neighborhood 

 of the growth. 



Agar-agar. The growth upon the surface of obliquely 

 solidified gelatin, agar-agar, or blood-serum is not luxuriant. 

 It forms a thin, moist, shining, translucent band with smooth 

 edges and a grayish-yellow color. 



Potato. When a potato is inoculated and stood in the 

 incubating oven, the typical growth cannot be detected 

 even at the end of the second day, unless the observer be 



* "Boston Med. and Surg. Journal," Feb. 13, 1908, CLVIII, p. 213. 



