Two surgical methods are described to derive bile and pancreatic juice separately by indwelling catheters in rats. 2. The secretes are always recirculated into the animals duodenum, the indwelling catheters forming an extracorporal loop. 3. The experiments are performed in the conscious animal. 4. The flow rate of the secretes is measured by drop-counting with resetting after a definite number of drops (staircase registration). 5. By interposed flow-through transducers several parameters can be determined f. i. by ion-selective-electrodes and microphotometers. 6. Additional analytic measurements can be carried out in samples. 7. There is a time-shift between the recorded curves corresponding to several different flow-through transducers placed one after the other in the extracorporal circuit of flow. This time shift is variable due to the dead spaces of the system and the actual flow-rate. The theoretical aspects of this general problem are discussed in detail. 8. Sampling of pancreatic juice causes immediately a pronounced increase of flow rate and the amount of protein secreted. Therefore, volumes taken must be given back quantitatively into the animals duodenum in order to avoid a disturbance of the normal secretion pattern.
