The osmotic pressure and chemical composition of human body fluids.

The total osmotic pressure (osmolarity) of each of a series of true body fluids has been measured and compared with that of the corresponding serum. Included were ascitic, cerebrospinal, hydrocele, edema, pericardial, pleural, spermatocele, and synovial fluids. In each case, the fluid was found to have the same osmolarity as that of the corresponding serum within the limits of experimental error. The conclusion has been reached that there is a law of constant osmotic pressure of all true body fluids (as distinct from secretions) and that this law holds whether the subject is biochemically normal or abnormal. Examination of the protein and ionic concentrations of these fluids strongly points to the conclusion that neither colloid osmotic pressure, increased capillary permeability, nor membrane damage can be the primary cause of these abnormal fluid collections. Some profound chemical differences have been demonstrated between the ionic composition of certain of these fluids and that of the corresponding serum. Additional evidence has been presented showing that intraand extracellular osmolarities are identical in the erythrocyte in a wide variety of abnormal cases.