34 SELMAN A. WAKSMAN AND JACOB S. JOFFE 



gelatin media and those containing glucose were sterilized in 

 flowing steam for thirty minutes on three consecutive days. In- 

 oculation was usually made from agar slants, by introducing a 

 small piece of growth into each tube. The cultures were then 

 incubated at 25° for fifteen days, unless otherwise stated. At 

 the end of the incubation period, the cultures were taken out from 

 the incubator and the H-ion concentration of the solution deter- 

 mined by the use of the phenol-disulphonic acid series of indi- 

 cators of Clark and Lubs (1917). The hydrogen-ion exponent, 

 the pH of Sorensen, rather than the concentration of the hydro- 

 gen-ions, is used in this work. The data on the growth and trans- 

 formation of nitrogen compounds of the studies given in tables 

 1 and 2 were reported elsewhere (papers II and III of this series). 

 Two grams of NaN0 3 and 30 grams of each source of carbon 

 were used per liter of medium in the first series of experiments, 

 reported in table 1. 



The data in table 1 clearly bring out the fact that the actino- 

 mycetes are not acid producers as so many bacteria are. The 

 source of nitrogen was such that it could not stimulate the pro- 

 duction of alkaline substances as would proteins through the 

 formation of ammonia and other basic substances; the carbo- 

 hydrates present were easily fermentable and readily convertible 

 into acids, but notwithstanding these two factors, the reaction 

 tended to change rather towards alkalinity than towards acidity. 

 The data in table 1 do not warrant us to say that any one actino- 

 myces produces always a change towards acidity of alkalinity or 

 that any one source of carbon is always changed in either direc- 

 tion. It was pointed out in paper II of this series that a greater 

 change in reaction (usually towards alkalinity) is observed with 

 a larger amount of growth and that the change in reaction seems 

 to coincide with the amount of nutrients (source of nitrogen 

 rather than that of carbon) removed by the organism from the 

 solution. It was suggested that the change in reaction towards 

 alkaline (increase in the value of the exponent designating the 

 hydrogen-ion concentration) may be due to the fact that the or- 

 ganisms remove the nitrate ions but not the sodium ions. But 

 this explanation will not hold in the light of the data brought 



