14 MAX LEVINE 



tively, while the strains from man and sheep vary in the other direc- 

 tion, lowering the averages to 0.67% for man and 0.68% for sheep. 

 It should be pointed out that the relatively high average for sewage, 

 0.83%, is due to the presence of Voges-Proskauer-positive organisms. 

 The average for the sewage strains exclusive of the Voges-Proskauer- 

 positive organisms, is 0.73% normal acid. Acid-production in maltose 

 can not be considered a reliable index for differentiation of Bacillus- 

 coli-like organisms from the sources studied. 



There is a rather marked and distinct relation between quantitative 

 acid-production in maltose and the Voges-Proskauer reaction. It 

 appears from Table 5 that the Voges-Proskauer-negative strains occa- 

 sionally form more than 1% acid, but usually less than 0.8%, while 

 the Voges-Proskauer-positive strains usually form more than 1% 

 and never less than 0.8% normal acid. The mode for the Voges- 

 Proskauer-negative strains is at 0.70% and the mean at 0.78% normal 

 acid. The mode and mean for the Voges-Proskauer-positive strains 

 are 1.10 and 1.12% respectively. 



ACID-PRODUCTION IN SUBSTANCES NOT FERMENTED BY ALL 

 THE TEST ORGANISMS 



The disaccharid, sucrose, the trisaccharid, raffinose, the glucosid, 

 salicin, and the alcohols, glycerol and dulcitol, were attacked by many, 

 but not by all, of the organisms studied. 



In calculating means and other constants for acid- formation, only 

 those organisms which attacked the test substances were included. 

 The line of demarcation for acid-production was selected at 0.4% 

 normal acid, because in sucrose, raffinose, and dulcitol organisms which 

 formed less than this amount in 36 hours at 37 C. rarely, if ever, 

 formed gas, while those which produced more than 0.4% acid, prac- 

 tically always formed gas also. 



A. SUCROSE 



In Table 6 are shown the frequency distributions of acid-produc- 

 tion in sucrose in relation to the MacConkey types, the source, and the 

 Voges-Proskauer reaction. The relation of acid-production to gas- 

 formation, and to the Voges-Proskauer reaction, is indicated, also, 

 in Plot 1. (One organism, which was overrun in titration, is not 

 included in the calculation.) Three modes are evident. One mode 

 is at 0.1% normal acid and represents those organisms which do not 

 form gas from sucrose. Acid-formation and gas-production in sue- 



