The calculated freezing point depression of freshly excised boiled mammalian tissue is approximately the same as that of plasma. The boiling procedure was chosen to eliminate the influence of metabolism on the level of the freezing point depression. Problems created by the boiling, such as equilibrium between tissue and diluent, change in activity coefficient by dilution, and loss of CO~ content, are discussed.A frozen crushed tissue homogenate is hypertonic to plasma. Boiling and dilution of such hypertonic homogenate exposed to room temperature for 5 to 15 minutes did not produce significant or unexplicable decreases in its osmotic activity. Moreover, freezing and crushing of a boiled diluted tissue did not produce any increase of the isoosmotic level of freezing point depression.It is possible to explain these data either with the hypothesis of hypertonic cell fluid or with that of isotonic cell fluid. In the case of an assumed isotonic cell fluid, data can be explained with one assumption, experimentally backed. In the case of an assumed hypertonic theory data can be explained only with the help of at least three ad hoe postulates. The data support the validity of the classical concept which holds that cell fluid is isotonic to extracellular fluid.

The freezing point depression of freshly excised frozen tissues, pulverized in a hydraulic press or in a mortar, is greater than that of plasma. Even at 0°C. the freezing point depression of such homogenates increases significantly with time. Dilution data indicate that such freezing point data are valid. The presence of intact cells has been shown in smears of tissues pulverized in a mortar, but not in smears of those crushed in a hydraulic press. The osmolarity of various diluent solutions affects the calculated osmotic activity of tissue homogenates presumably because of delayed diffusion between the diluent and cell fluid. With a hypertonic NaCl diluent, spuriously low values of tissue osmotic activity are found from calculations assuming instantaneous mixing between homogenates and diluents. The limitations of data from cryoscopic experiments and from tissue-swelling experiments are discussed in relation to the basic question of whether or not cell fluid is isotonic to extracellular fluid.

Changes in composition of renal solutes were studied in normal and in diabetes insipidus (D.I.) dogs subjected to varying degrees of solute (mannitol) loading. In both D.I. and hydropenic states, solute loading induced decreases in concentration of medullary solutes, and consequently decreases in corticomedullary gradients of solute concentration. The maximal level of papillary osmolality was associated with excretion of maximally hypertonic urine (nonloaded hydropenic states). The minimal level of papillary osmolality was not associated with excretion of hypotonic urine (D.I. states), but with excretion of slightly hypertonic urine during massive solute loading in normal hydropenic states. Hypertonicity of renal papillae (with respect to systemic plasma) even during excretion of hypotonic urine, together with a 7.6% vol of distribution of PAH in the papillae, indicates that final urine occupies only a small fraction of the renal papillary mass. Except for differences in location of peak concentrations, profiles of sodium and urea roughly paralleled those of total solute under all conditions. Decreases in papillary concentrations of sodium, induced by solute loading, paralleled those of osmolality in all cases. Decreases in papillary urea paralleled those of total solute (and Na) during loading in hydropenic dogs, but not in D.I. dogs. In the latter, concentration of papillary urea remained essentially fixed while those of Na and total solute decreased. In contrast to tissue concentrations of sodium and urea those of potassium increased in going from cortex to papilla under all conditions. The significance of these findings is discussed.

Data on barium-zinc filtrates of liver homogenates and of boiled liver indicate that the free glucose content of liver exceeds the blood glucose level. For instance, for boiled liver, the glucose level is 10.1, compared with a blood level of 5.4 mM/kg. Method of preparation of the tissue is important for the interpretation of the final results, as has been shown in appropriate control experiments. Various methods including paper chromatography were used to show that the reducing substance in liver is glucose. The relation of the high glucose content of liver to hexokinase activity, phosphate activity, and to glucose transport between liver cell and blood is discussed.