The dependence of normal plasma pH on sodium concentration in amphibians, reptiles and man.

Normal plasma pH at a given temperature is typically higher in freshwater turtles than in other reptiles, but lower than in amphibians. Normal pH in the different species at a given temperature shows a negative correlation with sodium concentration. Human plasma fits this pattern. What may be more nearly constant from species to species than plasma pH is the pH at particular sites on cell surfaces, and therefore the ionization of proteins located there.