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645the two tissues. High pyruvate concentrations inhibit LDH activity from either source to the same extent. The degree of inhibition by urea is always significantly less (p<.OO5) at the high (1 X M ) than at the low ( 5 X M) pyruvate level. Oxalate inhibits inguinal adipose tissue LDH less at the high than a t the low pyruvate level, while showing a reverse effect on the enzyme from pericardial tissue. Michaelis-Menten constants (K&I) for pyruvate were calculated from activities both in the absence and in the presence of urea and oxalate. KII values were significantly decreased in the presence of 2.0 M urea. All levels of oxalate studied increased the KM of pericardial adipose tissue LDH, but did not affect that of the inguinal adipose tissue enzyme, Incubation at 59°C for 10 minutes inactivates both enzymes to about the same extent, leading to a loss of 44 and 47% of their activity , respectively . Electrophoretic separation revealed 5 isozymes with a higher proportion of fast moving subunits in pericardial adipose tissue LDR.It gives the author pleasure to acknowlredge the skillful technical assistance of Miss Gail Crane.

Sodium and potassium contents of marrow cells, blood cells, and plasma were measured in normal rabbits and rabbits injected subcutaneously with phenylhydrazine to determine if small quantities of this chemical affected the ability of the blood and marrow cells to maintain their normal levels of these ions. There was a decrease in potassium content of red blood cells within 24 hr after administration of the compound, followed subsequently by a slight rise in plasma potassium. Apparently any effect was closely related to the time of blood sampling after the last injection, recovery occurring within several days if injections were not repeated at frequent intervals. The sodium and potassium analyses of normal bone marrow cells revealed differences in ionic concentration dissimilar to normal blood cells, the average sodium concentrations being higher and potassium concentrations lower in the former cells. Separation of marrow cells into three groups by prolonged centrifugation demonstrated a progressive increase in sodium and a decrease in potassium concentration from the lower to the upper stratum, possibly indicating a greater degree of ionic pumping in the more dense cells.