132 GENERAL MICROBIOLOGY 



the genus and species. Other valuable reference texts 

 are: 



CONN, ESTEN and STOCKING: Classification of Dairy Bacteria. 

 NOVY: Laboratory Manual of Bacteriology. 

 JORDAN: General Bacteriology. 



EXERCISE 44. EHRLICH'S METHOD OF TESTING 

 INDOL PRODUCTION 



The purpose of the exercise is to test the power of an 

 organism to produce indol from peptone. 



Cultures for comparison should be of the same age and 

 grown in the same kind of medium. Some peptones con- 

 tain a trace of indol and, to avoid all possibility of mis- 

 take when testing for indol, a control tube of sterile medium 

 should be used at the same time. This reaction is char- 

 acteristic for indol or for methyl indol (skatol). 



There are other tests for indol, but this one is by far 

 the most delicate. The Salkowski-Kitasato test (cone. 

 H2SO4 and NaNCb) will detect indol in a dilution of only 

 1 : 100,000, while Ehrlich's test will give a reaction in a 

 dilution ten times greater, or 1 : 1,000,000. 



Indol is one of the most important of protein decom- 

 position - products. It is noted for its intense fecal odor. 

 However, in highly dilute solutions it has the odor of orange- 

 blossoms, hence is used extensively in perfumery. The 

 jessamine blossom contains indol and has its odor. 



Indol has the following graphic formula: 



H 



UC/ C CH 



I D II 



H 



According to Emil Fischer, the reaction of Ehrlich's 

 test, produces, by means of the oxidizing action of the potas- 



