9 

 The source of indol in culture media is the amino acid tryptophane, 



NH 

 which is decomposed with the liberation of indol. 



NH 



Many of the irregularities reported are undoubtedly due to varying quan- 

 tities of tryptophane in the media employed and these may be eliminated 

 by use of tryptophane broth as suggested by Kligler. 



Motility. Motility may be determined either by the hanging drop 

 method or by the use of a semi-solid medium such as Hesse agar. In the 

 latter non-motile organisms grow along the line of inoculation with very 

 little diffusion into the medium whereas the motile organisms grow 

 rapidly away from the line of inoculation producing a distinct turbid zone 

 of several millimeters, in 6 to 12 hours, which may easily be observed 

 with the naked eye. 



There is considerable disagreement as to the value of motility as an 

 index and differential test for members of the colon group. There are 

 undoubtedly both motile and non-motile colon bacilli in the intestinal tract 

 of man. The character seems to be quite variable as a number of prelim- 

 inary cultures are sometimes required to make motility evident and 

 McWeeney has reported that some strains were motile at 20 degrees and 

 not at 37 degrees C. 



The statement that motile forms are characteristic of the human in- 

 testine appears to be in error as Stocklin (quoted by McWeeney) observed 

 116 non-motile strains among 300 colon bacilli from feces. Levine found 

 only 32 percent of 25 cultures from man to be motile and only 20 percent 

 of 30 cultures from raw and septic sewage whereas colon strains obtained 

 from animals were almost always motile (sheep 77.3%, cow 80.0%, pig 

 93.7%, and horse 100%). It should be noted that these results were ob- 

 tained with the use of a semi-solid agar (nutrient agar containing 0.5% 

 agar). 



The relation of motility as determined by the hanging drop and semi- 

 solid media has recently been studied by Chen and Rettger with results 

 indicated in Table II. 



It appears that for the true Bact. coli there is excellent correlation in 

 the two methods of motility determination. Out of a total of 173 cul- 

 tures examined, 119 strains were found to be motile by the hanging drop 

 method and 121 with the semi-solid agar medium. With the Bact. aerogenes 

 strains, however, out of 477 cultures observed, 122 were motile by the hang- 

 ing drop and only 75 by the agar method. It would seem that for the 

 aerogenes types observation of motility in semi-solid media is undesire- 

 able. 



