We have carefully analyzed the reaction in blood pressure that follows the injection of the various preparations. We find no constant effect. Digested secretin gives a fall in blood pressure that is at times less, at times equal, and at other times greater (Fig. 1) than that produced by the original preparation. Besides the bearing that it has on _the therapeutic use of secretin_, this destructive action of the digestive enzymes is also of prime physiologic interest. Failure to realize it has led to misconceptions as to the intrinsic nature of secretin. TABLE 3.--EXPERIMENTS 8 AND 9 Pancreatic Preparations Juice Drops Experiment 8: 10 c.c. secretin, five injections of inert depressor substances 29 10 c.c. secretin, two injections of completely digested secretin 28 10 c.c. secretin, eight injections of inert depressor substances 16 10 c.c. secretin 16 Experiment 9: 10 c.c. secretin (control, beginning of experiment) 21 10 c.c. secretin, after thirty minutes incubation with 1 c.c. _boiled_ gastric juice 27 10 c.c. secretin, after thirty minutes incubation with 1 c.c. _fresh_ gastric juice 11 10 c.c. secretin (control, end of experiment) 18 The findings of Lalou, confirmed by us, explain the anomaly that has led Delezenne[88] to put forward the antisecretin theory. [88] Delezenne and Pozerski: Jour. de Physiol., =14=:540, 1912. SECRETIN HAS NO ACTION WHEN GIVEN BY MOUTH It is a constant claim that so many and complex are the factors concerned in physiologic processes, that it is not unusual for clinical deductions to establish themselves in the face of _a priori_ laboratory dicta. We considered it desirable, therefore, to test the action of secretin, orally administered, in the most direct manner, and the one freest from possible criticism. With this in view, we performed a series of experiments on normal unanesthetized dogs having permanent pancreatic fistulas. _Method._--In the operations for permanent pancreatic fistulas we followed closely the technic developed by Pawlow,[89] and with excellent results. The dogs maintain themselves in splendid condition if proper care is taken. This consists in feeding them only with bread and milk, and giving sodium bicarbonate daily. The dogs were given this treatment in the evening so that experimental procedure might be carried on in the day with empty stomach under constant conditions. Freshly prepared secretin in large quantities was given by stomach tube to these dogs, and the response of the pancreas studied and compared with the response obtained from control preparations. The same preparation was generally not given on consecutive days.