256 CHEN CHONG CHEN AND LEO F. RETTGER 



The present investigation was planned with the following 

 points in view : 



1. To determine the relative frequency of the colon and 

 aerogenes types of bacteria in soils which from all appearances 

 are free from animal pollution. 



2. To ascertain whether or not there is a definite correlation 

 between types of bacteria and their origin. 



3. To make an extended correlation study of the coli and the 

 aerogenes types of gas-fermenting organisms with reference to 

 some of the most important reactions, particularly the gas ratio, 

 and the methyl red, Voges and Proskauer, and the uric acid 

 tests; and to determine the relative value of these tests in identi- 

 fication work. 



4. To determine the relative value of the following media in 

 the present correlation study: (a) The dipotassium phosphate- 

 glucose-peptone (Witte) medium of Clark and Lubs; (b) the 

 same medium with American brands of peptone in place of the 

 Witte; and (c) the synthetic medium of Clark and Lubs. 



5. To ascertain whether the coli and aerogenes types of bac- 

 teria change their character under prolonged cultivation in a 

 new environment. 



METHOD OF COLLECTING SAMPLES 



The samples were collected from four main sources in the 

 vicinity of New Haven, Conn., at different seasons and over a 

 period of two years. These sources are East Rock, West Rock, 

 Mt. Carmel and the New Haven Water-shed. In most instances 

 the samples were taken on the summits of the rocks or hills, and 

 in places far remote from human habitations. Chance con- 

 tamination from birds and wild animals cannot be excluded, 

 however, except perhaps when the samples were taken from 

 underneath precipices and rocks. Thorough sanitary surveys 

 were always made of the surroundings. 



Three types of soil were chosen: (1) those from open precipices, 

 (2) from between and under large stones, and (3) from well- 

 aerated open ground. They were selected in such a way as to 

 minimize as far as possible all chances of contamination. 



