A study of some of the literature with regard to the effect of hydrogen ion concentration on respiration, reveals that some investigators report maximum respiration a t a given pH, while others observe either a stimulation or depression of respiration with either an increase or decrease in acidity. For example, Brooks ('21) measured the CO, production of two species of bacilli and found a maximulm a t a p H of 7.0 and 6.8 respectively. Steward and Preston ('41) working with potato discs, noted that respiration ( a s well as protein synthesis and bromide ion absorption) was at a maximum at a p H of 7.0 and decreased as the solution was made either more acid or alkaline. Lyon ('27) observed a n increase in CO, output by Elodea canadensis as p H increased from 7.0 to 9.18, while, on the other hand, Thomas ( '31) working with carrot tissue noted an increase in respiration with increasing acidity. Lemmon ( '36) studying potato tissue found maximum respiration to result between pH's of 3.5 and 5.2 with a decrease in rate as the solution became either more alkaline or more acid. Also with potato tubers, Boswell and Whiting ('38) noted that oxygen uptake was essentially unaffected between pH's of 5.29 and 6.81. Oxygen consumption showed a slight decrease at pH values below 5.29 and an increase from pH 6.81 to 8.04.
Recently, Jeffrey ('51) has studied the effect of p H on the rate of oxygen uptake, and methylene blue reduction shown