254 CHEN CHONG CHEN AND LEO F. RETTGER 



brief period of but a few years most important advances in our 

 knowledge have been made. Some of the methods of earlier 

 investigators have given place to newer procedures which rest 

 on broader scientific foundations, as for example the differenti- 

 ation of types by exact methods of determining the hydrogen 

 ion concentration in media of known composition, and the 

 quantitative relationship of carbon dioxide to the total gas 

 volume. Again, older methods which had been practically dis- 

 carded have been re-applied and made to serve as very important 

 differentiating tests, as for example the Voges and Proskauer 

 reaction. 



In view of the claims held by many investigators that certain 

 types of colon bacilli met with in water have their origin in soil, 

 their occurrence in water being viewed only as the result of soil 

 washings, etc., the question of relationship of types becomes 

 all the more important. Correlation of characters with source, 

 according to such claims, is a problem which requires a most 

 careful and thorough solution, and if true correlation can be 

 established, careful colon bacillus typing will be an essential 

 part of sanitary water analysis. 



Both B. coli and B. aerogenes were long regarded as being of 

 fecal origin. Booker (1891), Hammerl (1897), Hellstrom (1901), 

 McConkey (1905 and 1909), Clemesha (1912), Rogers and his 

 co-workers (1914-16), Levine (1916), and others showed that 

 the aerogenes type is relatively infrequent in human and animal 

 dejecta, as compared with B. coli itself. Winslow and Cohen 

 (1918) estimate the frequency of B. aerogenes in animal feces 

 as to 2.6 per cent. 



The aerogenes type of colon bacilli appears to be widely dis- 

 tributed in nature, having as a rule a saprophytic existence. 

 Laurent (1899) thought that B. coli may lead a parasitic existence 

 on the potato. Klein and Houston a little later (1899-1900) 

 reported the occurrence of both typical and atypical B. coli on 

 grains of various kinds. Papasotiriu (1901) obtained results 

 similar to those of Klein and Houston. Prescott (1902 and 1906) 

 showed that coli-like organisms could be found on grains whose 

 contamination with fecal matter seemed very remote. Duggeli 



