A series of 13 bicarbonate and phosphate buffered Locke solutions was composed, the pH of which was determined. The increase of alkalinity, produced by warming these solutions from room temp. to 38[degree]C, is 0.1, and is therefore of practically no importance. Free aeration, as usually used in the Magnus method, generally turns all the bicarbonate buffered solutions more alkaline. While the Na2HPO4 has a marked stabilizing effect, the NaH2PO4 hastens alkalinization. With liberal aeration and agitation, presence of the contracting intestine does not materially affect the aeration curve; but with imperfect aeration as in the large tank, the ph takes the opposite direction (alkalinity is decreased). With the Magnus arrangement 0.008% NaHC03 is a sufficient buffer and maintains excellent functionation of the intestine over a long period. With less lively aeration, it is impossible to maintain a constant pH with bicarbonate buffers alone, but with 0.024-0.03% NaHCO3, the pH remains in the optimal range. If a constant p H is required, it might be maintained by the periodic addition of a bicarbonate solution (or by N/10 NaOH) under colori-metric control.