THE TYPHUS BACILLUS. 87 



given by Koch may be used. Stock cultures are prepared. 

 In the meantime the material to be examined is put in an 

 alkaline i per cent peptone solution and kept in an incu- 

 bator at 37 degrees. Within 6 to 12 hours the cholera 

 bacilli, if present, will have rapidly increased, 

 gathered at the upper surface of the fluid, at 

 times forming a fine film (on account of the great need 

 of oxygen). From the upper surface of the peptone so- 

 lution, or in other words, from the thin film, agar and 

 gelatine cultures are inoculated. After twelve hours 

 characteristic growths and reactions appear ; best on agar 

 at 2j'j degrees and on gelatine at 22 degrees. Regarding 

 the latter point a complete te.xt-book of bacteriology 

 must be referred to. It may be mentioned that the chol- 

 era bacilli grow only upon alkaline culture media, and 

 liquefy blood serum. They give a cholera red indol re- 

 action and have a remarkable tendency to dry up. 



3. THE TYPHUS B.\CILLUS. 



The Typhus bacillus is equally as difficult to demon- 

 strate in milk as is the exciter of cholera, particularly 

 since it is easily grown over by species very similar to it 

 and most always occurring together with it, for in- 

 stance, by the Bacillus coli communnis. 



For the difTerentiation of these two micro-organisms, 

 one utilizes, besides the different reactions with their 

 pure cultures (indol reaction, behavior towards sterile 

 milk, etc.), a culture process (method given by Eisner) 

 upon plates of potato gelatine mixed with i per cent po- 

 tassium iodide. Upon this media colonies of Bacillus coli 

 communnis appear after 24 hours as yellowish white 

 points, while at this period the Typhus bacillus will not 

 have grown. After 48 hours the Typhus Bacillus forms 

 small, bright glistening buttons (knobs'), while Bacillus 

 coli communnis forms large brown spots (specks). 



