BACTERIA OF THE COLON TYPE IN HUMAN INTESTINES 233 



samples came for the most part from men in normal health but 

 included two stools from infants. 



A small part of the sample taken at random with a platinum 

 loop was thoroughly shaken in a water blank and plates made on 

 asparagin-lactose-litmus agar (Ayers and Johnson 1915). These 

 plates almost invariably gave colon colonies only and since it has 

 been found that all types of colon bacilli grow readily on this 

 medium while streptococci do not, it is very well adapted to 

 isolation of these organisms from materials of this kind. 



Several colonies from each sample were transferred to lactose 

 broth and if gas was formed the broth was replated and a pure 

 culture obtained. In a few cases special means were taken to 

 favor the growth of certain types of colon organisms. 



Pigment formation. Very few grain cultures of B. coli are 

 entirely without pigment and many of them are decidedly chro- 

 mogenic. This property is correlated with other characters and 

 consequently is of value in classification. 



Chromogenesis was determined in the human feces cultures by 

 spreading on white paper the growth from an agar culture grown 

 twelve days at 20° and comparing with the plates in Ridgway's 

 Color Standards. It was found that this series was almost en- 

 tirely lacking in pigment. Nearly all of the cultures gave a 

 faint yellow color but this was so slight and showed so little 

 variation that it was of no value. There were, however, a few 

 exceptions to this statement. 



I ndol formation. Indol was determined by incubation at 30°C. 

 in a medium containing in 1000 cc. of water 0.3 gram tryptophane, 

 5 gram K2HPO4 and 1 gram of Witte pepton. The t3st for indol 

 was made by the p-dimethylamido-benzaldehyd-hydrochloric acid 

 method. The results are summarized in table 3. 



The liquefaction of gelatin. The test for gelatin liquefaction 

 was made by spreading about 0.5 cc. of a twenty-four hour sugar 

 free broth culture on gelatin held in a small test tube. This was 

 incubated twenty days at 20°C. No gelatin liquefiers were 

 found in this collection. This probably means that in these 

 samples at least, liquefiers occurred in such small numbers that 

 they were not isolated. There are numerous references in the 



