CHEMICAL PROPERTIES OF HAY INFUSIONS 275 
responsible. That the protozoa play a relatively small part in 
the acid production is shown in infusions D-1, E-1, and S-1, in 
which throughout their history practically no protozoa were 
present, and yet their acidity curves do not differ materially 
from the others of their respective series (tables 2, 3, 4). 
In order further to demonstrate that the bacteria are almost 
entirely responsible for the acid production, hay infusions were 
prepared and inoculated with pure cultures of bacteria as described 
on page 269. The results for ‘phenolphthalein acidity’ are 
recorded in table 6 (also fig. 5). It is apparent (especially for 
the B. coli infusions) that the acidity curves do not show any 
striking variations from those obtained from cultures promiscu- 
ously seeded with various forms of protozoa and bacteria. 
TABLE 6 
Phenolphthalein acidity. Bacterial infusions 
(Cubie centimeters 0.01 N NaOH per 100 ce. infusion) 
DAYS 
o| 1| 2 3) 4| 5| 6) 7] 8 9/10/11 12 19 2848 
Sreriletles ten tome Ie? lial alee tye fetal nee 7 6 6 7 
Peres Died <b. Heep ete eure | | 
Wola Nt ae A SiS iets) | 11) 0 8 8 8 5 
(Cia oe noes ra sea eae (balboa wa} |i | 9 | [eal 7) 6) 5 
Ge taS ak eye ew (LO 230 24129), | 22) S20 a Rie eel a0 
Cnlintie nen natn 20| 21| 20; | 20) | 19 | | 17 16) 14! 7 
Subpilis-lin of ig... 4 | 12} 10] 9) 7 Glan ies 6| 6| 6 6 
SUAS! fede ie ae salty | 8} 10) 8| 7 6 | 5 6 6 7 6 
From figs. 2 and 3, it is evident that the maximum difference in 
top and bottom acidity for series A is considerably less than the 
minimum difference for series C. Fig. 4 illustrates the maximum 
difference in series C. From table 3 it is apparent that in series 
B there is no essential difference between top and bottom acidity. 
The difference between acidity at the top and bottom of the 
infusion is probably to be referred to the unequal bacterial food 
supply in these two regions. In cultures of series B the food 
supply is uniform throughout the media, and hence acidity dif- 
ferences are not apparent. Where, as in infusions of series A, 
