74 JOSEPH HALL BODINE. 



that used by the gardener in ordinary greenhouse work. Total 

 volume of cultures varied from 2 to 5 liters, depending on size of 

 container used. When cultures were inoculated with organisms 

 samples were taken from several cultures so that as many repre- 

 sentative protozoan forms as possible were obtained. All cul- 

 tures were kept under the usual laboratory conditions, in the same 

 room, with the temperature as nearly constant as possible. 



The data obtained in such a study are most readily presented 

 by curves, since it is relative and not absolute changes in which 

 we are interested. 



Peters 1 and Fine 2 found that the top and bottom of cultures 

 varied in titratable acidity -at first, a high titratable acidity at the 

 bottom, and later, as diffusion proceeded, a more or less uniform 

 concentration was obtained and titratable acidity differences 

 tended to disappear. A similar condition has been found by the 

 author in titrations, but the differences in hydrogen-ion concentra- 

 tion are never great and, when occurring, last only for a very short 

 time in the early life of the culture. In the following results, 

 however, average conditions only will be given. 



Figure I shows graphically the changes in Ph in a typical soil 

 culture. These cultures, during the first few days,, become 

 slightly acid, followed by a less acid condition, and, finally, 

 remain rather alkaline throughout the remainder of the experi- 

 ment. Observation showed that organisms were most abundant 

 during the early life of the culture, when the change from a 

 slightly acid to a slightly alkaline reaction was taking place. 



Figure I also shows the changes in Ph in hay infusion cultures 

 prepared in slightly different ways. From these results it is 

 quite evident that the presence of hay, either boiled or unboiled, 

 tends to make a decided difference in the hydrogen-ion concentra- 

 tion of the culture. No attempt was made to keep the cultures 

 sterile, and since it has been pointed out repeatedly that the 

 bacteria are to a great extent, if not entirely, responsible for the 

 acid production, these changes in Ph between cultures with and 

 without hay are in all probability due to amounts of available 

 food for bacterial organisms, as well as to the acid-yielding con- 



1 Peters, A. W., 1907, Amer. J.OUY. Physiol., 17 and 18. 



2 Fine, M. S., 1912, Jour. Exp. Zool., 12, p. 265. 



