Filtration Through Living Membrane.

The mesentery of the bullfrog (Rana catesbiana) was used as the filtration membrane to test the rate of filtration of various fluids. The mesentery was so placed that a funnel could be easily approximated to it. This funnel led into a flask from which a glass tube connected with the vacuum pump and manometer and regulating stop cock. The animal was anesthetized with urethane. A catheter could be introduced into the bladder or into each ureter. This technic can also be applied to similar membranes in other animals.

During the experiment the flow of blood could be observed. Pulsation in some cases was readily visible at a pressure of 40 cm. of water. Even when no pulsation was visible, in some vessels at least, the flow of blood could be seen. Some membranes readily stand a pressure considerably in excess of 700 mm. of mercury; none broke at a pressure of less than 180 mm. of mercury.

The lack of uniformity in the rate of filtration with membranes of different frogs, and also the lack of uniformity in the slowing of the filtration, has necessitated thus far relatively short experiments and the counting of drops. The initial rate of filtration can frequently be restored by releasing the pressure at intervals and allowing the membrane to rest a few minutes. As a rule, with increased pressure there was an increase in the rate of filtration, but the relationship was not mathematical.

If the 0.8 per cent solution of sodium chloride is cold, the rate of filtration may decrease one-half, but will return to the initial rate if the fluid is warmed again. The difference in rate of filtration of fluids at room temperature and at higher temperatures was not striking.