304 MANUAL or BACTERIOLOGY. 



B. typhosus each show a characteristic, macroscopic appearance, so that they 

 can be separated from one another. Furthermore, the medium employed is 

 unfavorable to the growth of many bacteria hkely to be present. 



In agar containing milk-sugar and blue litmus the colon bacillus causes the 

 formation of red colonies each having a red zone, whereas the typhoid bacillus 

 forms blue colonies. 



The addition of crystal violet to the milk-sugar-litmus-agar inhibits the 

 growth of various organisms without materially affecting the growth of B. 

 typhosus. So the medium adopted after many trials was as follows : 



(o) Three pounds of chipped beef placed overnight in 2 Uters of water. 

 Strain off, and boil for one hour, filter and add 20 grams of Witte's peptone, 

 20 grams of nutrose, and 10 grams of salt. Boil one hour, filter and add to 

 it 60 grams of best stick agar; boil three hours over the flame or one hour in 

 the autoclave, make sUghtly alkaline to litmus paper, and boil one-half hour. 



(i) 260 c.c. litmus solution (Kubel and Tiemann); boil for ten minutes; 

 add 30 grams of c. p. milk-sugar, and boil the mixture fifteen minutes. 



(c) Add solution h to the hot, melted solution a; mix thoroughly and cor- 

 rect the reaction to weakly alkaline if not already so. 



{d) Add 4 c.c. of a hot, sterile 10 per cent, solution of dehydrated soda. 



(e) Add 20 c.c. freshly prepared ^^ per cent, solution of crystal violet (Kry- 

 stallviolet "B," Hochst). This solution should be made with warm, sterilized, 

 distilled water, but not boiled. 



A part of this agar is poured into Petri dishes at once. The rest is kept in 

 flasks, about 200 c.c. in each. 



The material to be examined is spread over the surface of the plates, not 

 mixed with the medium as is usually done, the object being to obtain surface 

 colonies only. 



The spreading is done by means of a glass rod 12 or 14 cm. long, bent at 

 right angles about 3 cm. from one end. The short arm of the bend terminates 

 in a small knob, and is dipped into the material to be examined and run over 

 the surface of the agar in a series of the previously prepared Petri dishes. 



Drigalsky-Conradi plates, as described above, are made from water by using 

 the precipitate after centrifuging. 



Ficker and Hoffmann* recommend the following method of treating the 

 material for examination for the typhoid bacillus before making the Drigalsky- 

 Conradi plates. They use an enriching fluid which has the property ,of in- 

 hibiting the growth of colon and other contaminating organisms, while not 

 seriously interfering virith the growth of the typhoid bacillus. 



This fluid consists of: 



(o) A stock solution of beef-broth. Take one kilogram of chopped beef; 

 add 2 Uters of distilled water; heat thirty minutes at 50° to 60° C; stir; boil 



* Ficker and Hoffmann. Weiteres iiber den Nachweis von Typhusbacillen. 

 Archiv jilr Hygiene. Bd. XLIX. 1904. 



