1. Inulin is filtered into the urine of Achatina fulica. The process is not subject to poisoning but water reabsorption may raise the U/B ratio to 2.8. The U/B ratios of substances actively reabsorbed or secreted reaches 1 when transport is poisoned thus verifying filtration as a first step in urine formation.

2. Exogenous urea is excreted by filtration.

3. Glucose is filtered and actively reabsorbed. Reabsorption can be poisoned with phlorizin.

4. Chloride is actively reabsorbed.

5. Phenol red and PAH are actively secreted. The secretory process may be poisoned with dinitrophenol.

6. The clearance of phenol red may be taken as an estimate of blood flow through the kidney, which may reach 5.6 ml./min./kg. in Achatina fulica.

7. The PAH clearance is depressed by simultaneous excretion of phenol red and the quantitative measurements of transport give evidence that the same secretory mechanism is used for both phenol red and PAH.

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