76 



being at the body temperature. In the following table is given the source 

 and treatment of the soil, crops raised, and the incidence of coli-like bacteria 

 in the samples studied.* 



It will be noticed that a number of plots which had not received 

 manure for many years (some about 15 years) yielded organisms of this 

 group. There was a marked correlation also between cropping and the 

 incidence of the colon group. 



TABLE XXXIX. PRESENCE OF BACILLI OF COLON GROUP IN EXPERI- 

 MENTAL SOIL PLOTS AT AMES, IOWA 



Of the 24 plots examined, 13 had been kept fallow and 11 had had 

 various crops, for the most part corn, raised upon them. Of the fallow 

 plots 7 (53.8%) showed no colon forms, in 2 (15.4%) such organisms 

 were rare, and relatively abundant only in 4 (30.8%). On the other 

 hand, bacilli of the colon group were readily isolated from each of the 11 

 plots upon which crops were grown. 



One hundred and seventy-seven strains were obtained in pure cul- 

 ture. Of these 142 (80.4% ) are of the aerogenes section (the predominating 

 type being the Bact. cloacae) and 35 (19.6%) are of the coli section. 



The preponderence of the aerogenes types in soil has recently been 

 confirmed in two very detailed studies by Burton and Rettger (1917) and 

 Chen and Rettger (1920). 



Burton and Rettger isolated 193 coli-like bacteria from about 1000 

 samples of soil, twigs, leaves, and flowers. 



Of these only 36 (18.7%) resembled Bact. coli whereas 157 (81.3%) 

 were of the aerogenes subgroup, 148 of the latter being Bact. cloacae. 



Chen and Rettger in a study of a large number of samples of soil 

 of known sanitary quality observed also a great preponderence of the aero- 

 genes section but they found the Bact. aerogenes rather than the Bact. 

 cloacae, as recorded by Johnson and Levine and by Burton and Rettger, 

 to be the predominating species. Of 467 strains studied, 430 (92.1%) 

 were Bact. aerogenes, 17 (3.6%) Bact. cloacae, and only 20 (4.3%) were 

 of the coli section (V. P. negative-methyl-red-positive type). 



The evidence is quite distinct and clear that the colon-like organisms 

 present in soil are of the aerogenes type and that they are more abundant in 

 cropped than in fallow areas. The relative incidence of the aerogenes and 

 coli sections in soil and grains is summarized in Table XL. 



