Abstract

The variations in the rate of absorption from the peritoneal cavity of fluid and solute from the different solutions investigated can be explained most simply as follows.

As soon as the fluid is introduced, free diffusion occurs between the fluid in the peritoneal cavity, and the blood, or the tissue fluids, and an equilibrium is reached when the peritoneal fluid contains 0.6 per cent NaCl, and a quantity of other substances, including proteins, which together produce a depression of the freezing point of about 0.2°C. This process of exchange is hastened by vaso-dilatation and slowed by vaso-constriction. The more rapidly the solute in the peritoneal fluid diffuses the more rapidly is this equilibrium attained, that is to say, the more rapidly is the solute absorbed.

At the same time absorption of the fluid may occur, and the rate of absorption is determined by the relation between the rate of diffusion of the substances producing the osmotic pressure of the blood, and the rate of diffusion of the substances in the peritoneal fluid. When, for instance, a solution of sodium chloride is introduced, the rate of diffusion of the chloride is greater than the average rate of diffusion of the constituents of the blood, and a fairly rapid absorption of fluid occurs, but by the end of an hour various slowly diffusible substances have entered the peritoneal fluid from the blood stream, and absorption becomes slower.

On the other hand, if a substance such as glucose is introduced, which has a very low rate of diffusion, then, since the rate of diffusion of the substance in the peritoneal fluid is lower than the rate of diffusion of the constituents of the blood, salts enter the peritoneal fluid quicker than they leave it, the osmotic pressure of the fluid rises, and little or no absorption takes place; after an hour much of the glucose has left the peritoneal cavity, but absorption still remains very slow, and the osmotic pressure is still higher than that of the blood.

No attempt is made to explain the absorption of fluids which are in complete equilibrium with the blood, such as serum, but the absorption of such fluids is comparatively slow, and any absorption due to these unknown causes would be masked, in the experiments described, by the more rapid changes due to the differences in the rate of diffusion.