Continuously Recording Radioactive Hemoglobinometer

A radioactive method, employing hemoglobin with incorporated Fe59, for continuously recording hemoglobin concentration in the blood of a living animal is described. This method records hemoglobin concentration independently of oxygenation of the blood and independently of the rate of blood flow through the apparatus. The only error that has been found in the method is statistical variation in the level of recording in accordance with the usual ``shot'' effect that is inherent in radioactive disintegrations. This statistical variation becomes less the greater the quantity of radioactive iron administered to the animal. For most purposes five microcuries per kilogram of Fe59 gives a satisfactory recording, and this quantity of radioactive iron is at least 50 times less than the maximal safe-handling dose.