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1. The absorption of (3)H- and (14)C-labelled palmitic, stearic and oleic acids under control conditions and in the absence of bile and/or pancreatic juice has been studied in sheep prepared with intestinal cannulae and reentrant fistulation of the thoracic lymph duct.2. Under control conditions the percentage recoveries in thoracic duct lymph of fatty acids introduced into the duodenum were: stearic acid 59.6 +/- 3.2 (mean +/- S.E. of mean), palmitic acid 71.1 +/- 1.2 and oleic acid 80.4 +/- 1.9.3. At the peak of absorption over 90% of the radioactivity was located in the triglyceride fraction.4. It was calculated that between 1900 and 3800 ml. lymph containing up to 20 g lipid flowed daily from the thoracic duct. The major fatty acids of lymph triglycerides were C(16:0) (26%), C(18:0) (39%) and C(18:1) (19%).5. In the absence of pancreatic juice, but in the presence of bile, the absorption of stearic, palmitic and oleic acids was 0.8, 4.-8.5 and 26% respectively of the dose injected into the duodenum. In the absence of bile but presence of pancreatic juice corresponding values were 0.1-0.5, 1.8 and 7.7%.6. In the absence of pancreatic juice the total lipid content of thoracic duct lymph fell from 800 to 80 mg% within 4 hr. When bile was also absent the lipid content of lymph fell further to 50 mg%.7. It is concluded that pancreatic juice functions in the lumen of the intestine probably through the production from biliary lecithin of the lysolecithin necessary for the optimum absorption of lipids.

1. The electrical properties of the resting and stimulated pancreas have been studied in the anaesthetized cat. There is an inverse relationship between the frequency of applied alternating current and the resistivity and dielectric constant of the resting pancreas. The resistivity is also affected by the fat content of the gland. The impedance locus of the pancreas is similar to that of other tissues.2. On intravenous injection of secretin there is a brief increase, followed by a more marked decrease, in conductance and capacitance of the pancreas. The phase of decreased conductance is related to the flow of pancreatic juice. The decrease in conductance and the flow rate can be characterized by two closely related empirical equations.3. During secretin stimulation the sodium concentration in pancreatic tissue increases, and the potassium concentration falls.4. It is tentatively suggested that the decreased conductance across the secreting gland is mostly due to swelling of the secretory cells and to a minor degree is the result of changes in the composition of the secretion in the pancreatic ducts.5. In the anaesthetized cat the mean half life of the secretory action of secretin is 199 sec.