METHODS

The experiments were performed on 3 healthy male subjects. Because of theirfamiliarity with the techniques and theory involved, all three are considered trained subjects. A dietaryhistory was obtained prior to an experiment. A standard single day's menu, closely approximating the usual diet, was then prepared with the collaboration of the subject. This menu was repeated each day of the study, subject only to modification of the salt or water content. One to two days before beginning the clearances, the subject was admitted to a private hospital room or to a metabolic study unit to become adjusted to thediet and to the routine of restricted activity, regular urine collection and other procedures. When the protocol was functioning smoothly, clearance measurements were begun.

Priming quantities of inulin and p-aminohippurate (PAH) were calculated to produce plasma concentrations of 30 and 1.5 mg per 100 ml, respectively. A sus-taining solution of 5 per cent inulin and 1.6 per cent PAH was injected intravenously at 0.6 to 0.7 mlper minute by a Sigmamotor pump through an indwelling plastic catheter. This solution, although supersaturated with respect to inulin, will remain clear for weeks if care is taken to avoid seeding with solid inulin. PAH was omitted from some experiments where avoidance of the additional sodium load in the PAH was considered more important than measurement of PAH clear-ance. When PAH and inulin were infused simultaneously, they were added to distilled water, the PAH con-tributing sufficient osmotic pressure to prevent hemolysis. 1 When inulin was infused alone, it was added to 5 per cent glucose. In some experiments powdered, refined inulin, 2 refiltered before use (43), was dissolved in the appropriate vehicle. In other experiments, commercial, ampouled inulin (Warner-Chilcott) was employed. Since this inulin is prepared in saline, a quantity sufficient for 24 hours' infusion contains 2.5 g of sodium chloride and an amount of salt approximating this quantity was re-moved from the patient's diet. The infusion was delivered to the subject through a 10-to 12-foot length of small-bore Tygon tubing which permitted free ambulation within the confines of the study room. Although the subjects were relatively inactive, they were not confined to bed. Clearance periods were generally of 3 hours'