NOTE OX THE IXOR(i.\XIC' PHOSPHATE OF BLOOD PLAS.MA 



468 



That protein bound inorganic phosphate is present in small amount 

 only in the serum of the dog is also borne out by the work of Smith et al. 

 (1943) who determined the percentage of ultrafilterable inorganic serum 

 phosphate in 13 cases. The average percentage of ultrafilterable in- 

 organic P found in their experiments works out to be 96%. 



Table 1. — Inorganic P Content and Activity of Plasma 

 Samples Secured from the Dialysator at Various Times 



Time in liours 



luorgaiiip i' ooiiteut in relitive Activity in relative units (100 

 units(100 relative units^.i. 7 mgm%) relative units = 200 counts per miii 



1 Extracted at 20°. 



2 Extracted at 0°. 



Not only a combination with proteins, but also the formation of 

 colloidal phosphate will prevent ultrafiltration of inorganic P or its 

 removal into the electrodialysate. Grollmaist (1927) found in an early 

 work that, while the inorganic P of normal pig serum is entirely ultra- 

 filterable, a successive increase in the calcium content of the plasma 

 from 9.4 to 32.2 mgm % makes the inorganic phosphate less and less ultra- 

 filterable and, finally, only 5% are found in the ultrafiltrate. Ample 

 evidence was brought by different authors that only excessive quan- 

 tities of calcium phosphate salts lead to the formation of detectable 

 amounts of a colloid complex (cf. Schmidt and Greenberg, 1935 ; 

 McLean and Hindrichs, 1938). 



GovAERTS (1943, 1947) compared the specific activities of the in- 

 organic P of plasma and urine shortly after intravenous injection of 

 labelled phosphate into the dog. In the first li/, hours, the specific 

 activity of the urine P was found to be greater than the corresponding 

 value of the plasma P ; after the lapse of that time no difference was 

 found. GovAERTS interprets these results as indicating that the greater 



