244 



Bacteriology of the Soil 



malignant edema, in addition to which, however, there are a great 

 variety of organisms pathogenic for rabbits, guinea-pigs, and mice. 

 In the " Bacteriological Examination of the Soil of Philadelphia," 

 Ravenel* came to the conclusion that 



1. Made soils, as commonly found, are rich in organic matter and excessively 

 damp through poor drainage. 



2. They furnish conditions more suited to the multiplication of bacteria 

 than do virgin soils, unless the latter are contaminated by sewage or offal. 



Fig. 86. Tip of Frankel's instrument tor obtaining earth from various 

 depths for bacteriologic study. B shows the instrument with its cavity closed, 

 as it appears during boring; A, open, as it appears when twisted in the other 

 direction to collect the earth. 



3. Made soils contain large numbers of bacteria per gram of many different 

 species, the deeper layers being as rich in the number and variety of organisms 

 as the upper ones. After some years the number in the deeper layers probably 

 becomes proportionally less. Made soils are more likely than others to contain 

 pathogenic bacteria. 



In seventy-one cultures that were isolated and carefully studied 

 by Ravenel, there were two cocci, one sarcina, and five cladothrices; 

 all the others were bacilli. 



* "Memoirs of the National Academy of Sciences," First Memoir, 1896. 



