The work herein reported was undertaken to test the amount of inorganic calcium and phosphorus in the blood of horses.
The same rates for blood calcium reported by Dünnemann: 11 to 13 mg. per 100 ml for serum were faund.
In horses from 3 to 3,5 years old the inorganic phosphorus content per 100 ml. of blood serum varied from 2,05 to 5,5 mg, the average rate being 4 mg. It is suggested any variation above these figures be considered as abnormal.
In adult horses the blood serum phosphorus content varied from 2 to 3,36 mg. per 100 ml., the average rate being 3,5 ro. As in the blood serum phosphorus content in the younger horses, any variation froro these figures might be considered as abnormal.
There were no difference in the calcium and phosphorus rate of the blood of pure bred race horses and crossbred horses analized.
No significant variation was found in the inarganic calcium and phosphorus content oí the blood in relation with the age of the animals analized nor in relation with sex.
The fine filter paper used, in spite of its purity, contained little amount of phosphatus which produced a definite variatian in the results of the colorimetric determination of ignarganic phosphorus. This source of error was avoided by doing the desalbuminization of the plasma or serum by centrifugation instead of filtration. Besides this atable of error was built up to be used as correction factors in the colorimetric determination of inorganic phosphorus which may serve to research man as a guide.
The results obtained were not accurate when hemolizzed serum was used.
The rate of calcium was always lower when this kind of samples were used.

1 Director del Instituto de Investigaciones Veterinarias
2 Médicos Veterinarios