COLON-AEROGENES GROUP OF BACTERIA 259 



For an organism to be admitted into the final collection of 

 strains the following recognized characteristics were required. 

 They must be short rods, staining readily with the ordinary dyes 

 but not by the Gram method. They must fall in the class of 

 non-spore-forming organisms, and possess the ability to attack 

 lactose with the formation of acid and gas. 



Altogether 467 strains were obtained from the various soil 

 samples. Of this number 447 were finally identified as belonging 

 to the aerogenes-cloacae subgroup or type, while the remaining 

 20 were designated as typical B. coli. 



For comparative study the same types of organisms were 

 sought in human and animal feces, and 173 coli-like organisms 

 were isolated from the feces of 7 men, 2 monkeys, 4 horses, 3 

 cows, 4 sheep and 3 fowls. No organisms of the cloacae-aerogenes 

 type were found, all of the isolated strains proving to be typical 

 B. coli. This should not be regarded as evidence that the aero- 

 genes-cloacae type is not present in the intestines of man and 

 animals. It does indicate, however, that they are of uncommon 

 occurrence there. 



The table on page 258 contains a summary of all the samples 

 taken from soil and human and animal feces, showing the number 

 of strains obtained and the types of organisms isolated from each 

 source. 



MORPHOLOGY, STAINING PROPERTIES AND MOTILITY 



When grown on plain agar the large majority of the strains 

 were alike within narrow limits, and resembled in size and form 

 ordinary B. coli, being distinctly rod-shaped, with rounded ends. 

 Some strains were thicker than others, and frequently short 

 forms were observed which were more or less coccus-like. All 

 strains were Gram-negative, although some took the counter- 

 stain more deeply than others. All took the ordinary stains 

 readily. Spore formation could at no time be demonstrated. 



Motility studies were made on twenty-four hour cultures, 

 grown in Clark and Lubs' medium, and for the greater part of 

 the time by the hanging drop method. The Hesse method of 

 cultivation in semi-solid agar was also employed. While in 



