62 BACTERIA 



appears almost at once, and may be accentuated by placing 

 the culture in the blood-heat incubator for half an hour. 

 Much dextrose (derived from the meat of the broth) inhibits 

 the reaction. Bacillus typhosus does not produce indol, and 

 therefore does not react to the test ; B. coli and the bacillus 

 of Asiatic cholera do produce indol, and react accordingly. 

 It should be pointed out, ho\yever, that the bacillus of cholera 

 also produces nitrites. Hence the addition of acidonly to a 

 peptone culture of cholera yields the *' red reaction" of indoL 



2. Carbolised Gelatine. To ordinary gelatine .05 per cent, 

 of phenol is added. This inhibits many common water 

 bacteria. 



3. ** Shake Cultures'' To 10 cc. of melted gelatine a small 

 quantity of the suspected organism is added. The test-tube 

 is then shaken and incubated at 22"" C. If the organism is 

 Bacillus coli, the next day reveals a large number of gas- 

 bubbles. 



4. Eisner s Medimn. This special potassium-iodide-potato- 

 gelatine medium is used for the examination of typhoid 

 excreta. It is made as follows : 500 grams of potato 

 gratings are added to 1000 cc. of water ; stand in cool place 

 for twelve hours, and filter through muslin; add 150 grams 

 of gelatine ; sterilise and add enough deci-normal caustic 

 soda until only faintly acid ; add white of ^^^ ; sterilise and 

 filter. Before use add half a gram of potassium iodide to 

 every 50 cc. Upon this acid medium common water bacteria 

 will not grow, but Bacillus typhosus and B, coli flourish. 



5. Parietti's Formula consists of — phenol, five grams; 

 hydrochloric acid, four grams ; distilled water, 100 cc. To 

 10 cc. of broth 0.1-0.3 cc. of this solution is added. The 

 tube is then incubated in order to see if it is sterile. If 

 that is so, a few drops of the suspected water are added, 

 and the tube reincubated at 37° C. for twenty-four hours. 

 If the water contains the B. typhosus or B, coli, the tube will 

 show a turbid growth. 



