When myohemoglobin is injected intravenously into dogs, in amounts ranging from 0.75 to 1.50 gm., it is rapidly eliminated from the plasma and approximately 65 per cent is excreted by the kidneys in from 1½ to 2½ hours.

Myohemoglobin does not appear in the urine below a threshold plasma concentration which is slightly under 20 mg. per 100 cc. but above this level the rate of renal excretion is directly proportional to the plasma concentration.

The maximum myohemoglobin/creatinine clearance ratio averages 0.58 contrasted with a value of 0.023 for blood hemoglobin. This indicates that the rate of renal clearance of myohemoglobin is twenty-five times more rapid than that of blood hemoglobin. Evidence is presented that the excretory mechanism is essentially similar for the two substances but that differences in molecular weight account for different rates of glomerular filtration.

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