SUMMARY1. The relations between motility, tone, water absorption rate (J,) and lymph flow (J,), were studied in an exteriorized upper jejunal preparation in vivo, with its serosal side bathed in Krebs-Ringer or other solutions. Neither J, nor J, was correlated with motility.2. When the luminal fluid consisted of an isotonic solution of MgSO4, glucose or LiCl, motility was greatly increased with no increase in J1.3. When the serosal fluid consisted of an isotonic solution of mannitol, glucose or MgSO4, motility was depressed with a large decrease in tone, and J, was increased by 51-83 % with a decrease in J,. When the serosal fluid consisted of an isotonic solution of NaCl, Na2SO4, LiCl or KCl, motility was decreased with either no change or an increase in tone, and both J, and J, were much decreased. When isotonic cholihe Cl solution was employed as the serosal fluid, motility increased with an increase in tone, J, became negative (fluid secretion), and J, decreased to 0. 4. Acetylcholine depressed motility but increased tone with a decrease in Jv and J,. Eserine increased both tone and motility with a decrease in Jv and Ji. Serotonin caused no change in motility but increased tone with a decrease in J4 and J,.Noradrenaline and adrenaline depressed motility and reduced tone with an increase in Jv and Ji. Isoprenaline abolished motility and reduced tone with a large increase in Jv but no change in J,. Pentobarbitone depressed motility and reduced tone with an increase in Jv but a decrease in J,.5. It is concluded that the intestine responds to various stimuli with a change in motility, or tone, or both. Intestinal motility per se does not produce lymph. Since an increase or decrease in tone always results in a decrease or increase in J, respectively, regardless of the nature of the conditions, a relaxation of the intestinal musculature appears to be associated with an increase in water absorption.

A newly developed intestinal preparation is described for determining lymph capillary pressure (PL) in the villi in vivo and in vitro. Determination of PL provided an estimate of tissue fluid pressure in the villi. PL was related to the fluid absorption rate and increased by lymphatic obstruction. During fluid absorption from isotonic mucosal fluid, PL was 1.4 +/- 0.5 or 1.1 +/- 0.4 cmH2O determined in vivo or in vitro, respectively. Both pressures were essentially in the same range as that (0.7 +/- 0.3--1.3 +/- 0.5 cmH2O) in which the mucosal fluid was isotonic Na2SO4 solution or Na-free solutions from which little fluid absorption occurred. This range of pressures may be taken as the normal tissue fluid pressure in the villi. At a high rate of fluid absorption from hypotonic mucosal fluid, PL increased to 5.2 +/- 1.4 cmH2O and tissue fluid pressure was also similarly increased. It is concluded that the fluid absorptive process by the epithelium could not develop an appreciable hydrostatic pressure in the villus tissue space or in the lymphatics.