NOTES ON THE BACTERIOLOGICAL EXAMINATION OF THE SOIL OF 



PHILADELPHIA. 



By Mazvck P. Ravenel, M. I). 



Scott Fellow in Hygiene, 189S-94. 



Presented by Dr. J. S. Billings. 



This work was undertaken at the instance of Dr. John S. Billings, Director of the Laboratory 

 of Hygiene, University of Pennsylvania, with the view of obtaining, if possible, some explanation, 

 from a bacteriological standpoint, of the greater mortality among persons living in houses built 

 on made ground over those living on virgin soil. In some cities, as Washington and New York, 

 filled localities can be mapped out and the course of old runs followed by the higher death rate 

 in these districts. No positive opinion can be based on the data so far obtained, and these notes 

 are presented mainly as a small contribution to our knowledge of the bacteria of the soil. 



In the prosecution of the work I have had the advice of Dr. Billings and of Dr. A. C. Abbott, 

 first assistant, to both of whom I am much indebted. 



SUMMARY. 



The work has extended over a period of ten months, with considerable interruption during 

 much of the time. 



Virgin soil was examined to a depth of 12 feet, samples having been obtained from the walls 

 of an excavation at intervals of a foot. Samples of made soil were obtained in the same way 

 to a depth of 9 feet. Other samples of both made and virgin soil were obtained by Fraukers 

 earth borer to a depth of 5J feet. 



From these samples of earth 71 cultures were isolated and carefully studied. Wherever 

 possible they were ideutitied with already described species, aud with each other, the final result 

 being .'50 varieties of organisms, of which 21) are believed to be new. 



Morphology. — The bacillus forms predominate largely. (Inly two cocci were found, both new. 

 No spirilla were found, and but one sarcina. Five varieties of cladothrix were found, only one of 

 which has been identified with already described species — the Cladothrix dichotoma of Colin. 

 This species has been found repeatedly at different depths in both made and virgin soils, being 

 apparently the most common and widely distributed form of the genus. 



Depth. — The greatest depth at which bacteria have been found in virgin soil was <> feet, at 

 which depth the bacillus Megatherium and the bacillus ramosus were observed. All samples of 

 virgin soil below this were found to be sterile. 



This result agrees closely with the experiments of Koch and Friinkel. The former in 1881 

 found that few bacteria were to be found 1 meter below the surface in soil which had not been 

 disturbed. Friinkel found that the number of organisms decreased greatly and suddenly at a . 

 depth of three fourths of a meter to li meters, while at the latter depth life was absent in 

 many instances. He obtained, however, in other experiments, colonies from a depth of 3 and 4 

 meters, which took a long time to make their appearance (Sternberg). Only one of the varieties 

 most commonly found by Friinkel in the deeper layers of the soil was encountered in these 

 experiments, the bacillus ramosus. In two experiments a sterile layer was found at the depth 

 of about 1 meter, below which a considerable number of bacteria were observed. 



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