Quantitative Studies of the Composition of Glomerular Urine

In view of existing evidence that inorganic phosphate of serum is capable of passing through membranes impermeable to protein, and in view of the increasing volume of evidence that glomerular urine has the composition of an ultrafiltrate, it is difficult to believe that part at least of the inorganic phosphate of urine is not excreted through the glomeruli. In compensation dialysis experiments, Rona and Takahashi (1) found phosphate of horse serum to be completely diffusible. Cushny (2) found 3.9 mg. per cent of phosphate phosphorus in an ultrafiltrate of ox serum. Neuhausen and Pincus (3) filtered pig serum through collodion and found slightly higher values of inorganic phosphate in the filtrate than in the serum. Grollman (4) found that 100 per cent of the inorganic phosphate in normal pig and dog serum was filtrable; in frog serum, 85 per cent. He was able to decrease t.he filtrability of phosphate by the addition of calcium chloride to the serum. That the fluid separated from the blood in passing through the glomerulus has the composition of an ultrafiltrate is shown by the