In the frog sartorius muscle, the effects of ouabain and no external K ions were comparatively investigated, although both caused apparently similar effects on active transport of Na ions. Washout experiments of isotopic Na and flamephotometric determinations of internal ions were made with reference to the effluxes of other ions or to mechanical properties. The changes in these parameters were examined when ouabain was added to or external K ions were eliminated from a bathing solution. The effects of them on Na effluxes from the muscle with normal Na and that with higher Na were also compared. 1. The effect of ouabain was different from that of external K withdrawal with respect to either time dependency or concentration dependency of the change in ion contents. This discrepancy was also held for the effect on muscle contractility. 2. Ouabain gave influence on net loss of K⁺ in K free Ringer more intensively than on the exchange efflux of K⁺ in Ringer. When external K ions were removed or ouabain was added the ²²Na efflux was roughly halved, however, the depressive effects were taken place independently. Ouabain demonstrated the concentration effect on the reduction in ²²Na efflux but not on the change in ion contents. 3. ²²Na efflux which had been reduced in K free Ringer was recovered to the normal level by a simple addition of external K even after very long immersion; the mechanism to restore K-dependent Na efflux could be left unchanged for such a long period as 24 hours in the absence of external K ions. This typeof recovery was observed without any relation to external Na ions. 4. In addition to the portion of active Na efflux sensitive to external K, there was ouabain-sensitive Na efflux portion separately. Ouabain showed no interference with the effect of external K on Na efflux. The depressive effect of ouabain on ²²Na efflux was also detected in the medium without external Na ions, 5. The mode of the action of ouabain on Na efflux was explained in the fashion different from that of withdrawal of external K ions. The effects of both could not be interpreted by the simple competition for the same site of membrane. The decrease in pump activity caused by removing external K ions was long maintained in a state that a simple addition of K ions promptly resulted in the resuscitation of the pump activity, while the decrease in pump activity by ouabain was followed by qualitative change in the pump machinery.

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The classical view of digestion holds that proteins and polypeptides are completely broken down to individual amino acids before absorption from gastrointestinal tract. Little information has been available concerning absorption of peptides. It is known that γ-globulin and some polypeptides can be absorbed without any enzymatic degradation from intestinal mucosa of neonatal animals but not in adult ones. In recent years, some workers (Agar et al., Newey et al., Wiggans et al.) observed absorption of small peptides in animal preparations. Further studies revealed that some protein hormone such as insulin and proteolytic enzymes can be absorbed in its natural form, and the latter are now used orally in certain patients with considerable effect. It is of great interest to elucidate the mechanism of transport of peptide by the intestine. This study is concerned with the absorption of reduced form ³⁵S-GLUTATHIONE (γ-L-Glutamyl-L-Cysteinyl-Glycine, GSH) from rat intestine in vitro and in vivo and the incorporation of the label into protein.

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