S7 TABLE 11 Subject Feces Urine Body burden puc Cs'37 pyc C53? gk gk C Daily excretion 2 x (urine) +0.5 (feces) upc Cs9? B 5 825 575 0.22 412 + 1,150 = 1,562 8 1040 638 0.41 520 + 1,276 = 1,796 IV. Exchangeable Potassium in Humans C.E. Miller The measurements of exchangeable potassiurn in humans are based on the following simplified model. The normal K present in humans is con sidered to be present in two fractions or pools. The atoms of K in one poo are bound within the cells and are not immediately replaced by other atom: of K from the blood stream. The atoms of K in the second pool are exchan able and are constantly being replaced by new atoms of K. The K present : the urine has thus originated from the exchangeable K pool. . The exchangeable pool is measured in the following fashion. Each subject is given 5 yc of K** at 9:00 A.M. All urine voided from 9:00 A.M. until 10:00 P.M. is collected in one vessel and the amount of K** eliminate recorded. The first void the next morning is collected in a second con- tainer, and all urine voided thereafter until the subject is measured is collected in a third container. The amount of K* present in the body at an time is thus known. All K** has been mixed into the pool of exchangeable I by the definition of exchangeable K. The ratio of K** to normal K present ; the urine the following morning should equal the ratio of K** to normal K present in this so-called exchangeable pool. The amount of K* present in the urine determined by gamma-ray analysis, and the amount of normal K present is measured with a flame photometer. The amount of K presentir the exchangeable pool is found by multiplying the K*? present in the body b the ratio: a 7 normal K in the urine K* in the urine This value of K is then compared with the total body potassium as measur bv the in vivo gamma-ray techniques. | On the basis of repeated tests performed on five subjects it can be said that the exchangeable potassium is of the order of 90 per.cent or mor of the total potassium. It seems certain, however, that because of either 3012131