RENAL FUNCTION 253 



logical experiments performed. It is suggested that the source of the 

 pressure is the arterial blood pressure, the kidney of the gastropod receiv- 

 ing afferent renal blood vessels directly from the ventricle of the heart. 



Kidney 

 Pericardial sac 

 Kidney duct 



ACHATINA FULICA 



Fig. 1. Appearance of a specimen of Achatina julica prepared 

 for sampling from pericardial sac, kidney lumen, and kidney duct. 



In addition to a catheter in the kidney duct which permitted quantitative 

 collection of urine, a soft plastic catheter was tied into the perivisceral 

 space, entry being made under ether anaesthesia through the foot. Inulin 

 was injected at regular intervals and blood and urine samples collected 

 alternately for long periods of time. In those experiments in which the 

 urine was allowed to flow freely from the catheter, the urine/blood inulin 

 ratio was usually one and remained nearly so at high rates of urine flow. 

 Continuous reabsorptive and secretory processes were taking place during 

 this time, as was shown by the reabsorption of glucose and the active con- 

 centration of injected dyes. The poisoning of reabsorptive or secretory 

 processes brought the U/B ratios of such substances close to that obtained 

 simultaneously for inulin. These results are most satisfactorily under- 

 stood on the assumption of a process of filtration. 



A free flow of urine from the kidney of the snail is probably a rare 

 occurrence in nature. The presence of a tortuous duct and muscular 

 sphincters will allow for much water reabsorption under conditions where 

 water conservation is important. It is well known that hibernating snails 

 may produce no urine w^hatsoever. The effects of such back pressure may 

 be illustrated in the following experiment. A tightly fitting catheter was 

 tied into the kidney duct and the preparation tested for leaks by the injec- 

 tion of faintly colored water. The urine collection was then carried on at 

 known elevations at or above heart level, thus producing a back pressure 



