1. Comparative studies of blood serum and edema fluid from the same individual indicate that, regardless of the pathological condition present, whether the fluid be "transudate" or "exudate," certain definite qualitative chemical relations obtain.
2. The chief feature of these relations is that the edema fluid contains more Cl and less K than the blood serum; while the Na, HCO3, Ca, urea, glucose, and non-protein nitrogen exist in approximately the same concentrations in the serum and in the edema fluid. The freezing point is also the same in both fluids, while the specific conductivity is constantly higher in the edema fluid.
3. The above mentioned variations between the edema fluid and the serum appear to be related to the difference in the concentration of protein in the two solutions.
4. The relationships between blood serum and edema fluid seem to result from a simple membrane equilibrium, influenced in part by the proteins present.