CHEMICAL PROPERTIES OF HAY INFUSIONS 281 
detailed correlations are not possible. It is my opinion from this 
study that even did we know exactly the course of the curves 
illustrating mineralization, oxygen consumed, acidity, alkalinity 
and other information of a general character—with such data 
alone nothing but the most superficial correlations could be 
expected. It is not improbable that a partial explanation of the 
sequence of protozoa occurring in hay infusions may be found in 
the influence of certain excretory products of an organism upon 
others of its own or other species. That this is a consideration of 
some importance is brought out in a recent paper by Woodruff,” 
in which it is shown that the excretory products of paramaecia 
inhibit the reproduction of these organisms. 
SUMMARY 
The acidity of hay infusions is essentially due to bacteria, 
their efficiency in producing acid being governed by the concen- 
tration of the infusion in acid-yielding materials. The protozoa 
play a relatively small part in the production of acid. The 
sequence of protozoa and the course of the titratable acidity possess 
no intimately mutual relation. Either may vary within wide 
limits without appreciably influencing the course of the other. 
' Woodruff: Jour. Exp. Zool., vol. 10, p. 557, 1911. 
