Abstract
Normal rabbit diet contains 45 p.p.m. of free nitrate. Replacement of this diet by one containing ten times less free nitrate resulted in a decrease in size and eventual loss of the signal. Addition of potassium nitrite to the drinking water of animals with no 2.03 signal resulted in the formation of such a signal and an increase in its size until it was equal to, or greater than, the average from rabbits on normal diet. Addition of nitrates to drinking water did not give rise to a g=2.03 signal, but to a characteristic triplet signal with a g=2.012. Chemical treatment of the various liver fractions showed that the g=2.03 signal, in pure form, could only be formed in the cell sap fraction. The possible origin of the various signals is discussed.