280 MORRIS S. FINE 
may possibly be accounted for by the difference in the quality 
of the tap waters used in the two investigations. For example, 
the tap water employed in our experiments titrated 6 cc. 0.01 
N HCl per 100 cc. of sample, while water from a neighboring 
well titrated 22 cc. per 100 ce. of sample. 
RELATION OF TITRATABLE ACIDITY TO PROTOZOAN SEQUENCE 
The organisms make their appearance at about the same time 
in the three types of infusions. The protozoa of the B series run 
their course more rapidly than those of the A and C series, the 
two latter not varying markedly in this respect. These time 
relations are probably in great part dependent upon the food sup- 
ply. The latter is the determining factor for acidity. However, 
the degree of titratable acidity existing in an ordinary hay infu- 
sion has no important bearing on the duration and character of 
the cycle taking place, for in the three types of infusions, the 
sequence of the dominant protozoan forms studied was the same, 
although these culture fluids show characteristic differences in 
the degree of acidity. Furthermore, the cycle normally occurring 
in the B series was not influenced when the acidity was purposely 
increased to two or three times that ordinarily obtained.!4 When, 
however, the acidity was raised to seven or eight times that of the 
typical B infusion,“ the development of the protozoan fauna 
was greatly retarded. Decreased acidity, likewise, has no appre- 
ciable influence upon the protozoan cycle: BB-5 had an almost 
negligible acidity” throughout its history, yet the sequence of 
organisms did not differ in any important respect from that 
found in the control infusion, BB-6, or other typical infusions of 
this series.'° 
While certain species of protozoa are particularly abundant 
during the period of high acidity and others during low acidity, 
13 Cf. Woodruff, loc. cit. 
144'This was accomplished by adding dextrose to the infusion. Cf. p. 268 and 
table 3. 
1 Brought about by adding alkali when necessary. Cf. p. 268 and table 3. 
16 The biological examination of infusions BB-1 . . . . BB-6 was made 
by Dr. Woodruff but not reported in his paper. 
