Observations on the Perfused Living Animal (Dog) Using Homologous and Heterologous Blood

An examination of the condition of the perfused living animal preparation has included measurements of vascular resistance, pulmonary ventilation, responsiveness of the heart auricles, blood vessels, bronchi and respiratory muscles to direct and reflex stimulation, and persistence of respiratory centre activity. 2. These measurements and measurements of blood levels of sugar, lactate and pH, supplemented by post‐mortem histological examination, showed that the condition of the animal during perfusion is in all its main signs that of peripheral circulatory shock, and that the condition becomes progressively worse in the later stages of perfusion. 3. There was nevertheless often an initial period of relative stability which might continue for as long as 5 or even 7 hours, during which the circulating blood volume remained constant, vascular and respiratory reflexes were present, respiratory centre discharge was regular, and when pulmonary vasomotor nerve responses were constant and reproducible. 4. Acidæmia, due to a high lactic acid production, was present in all the experiments; over the range of blood values found only pulmonary vasoconstrictor responses were observed. Biochemical changes in the blood, the physiological responses to stimulation and the degree of shock and/or tissue damage were not significantly different if horse instead of dog blood were mixed with the recipient's blood for the purpose of perfusion. 5. The effects, which may be primarily due to traumatic shock and anæsthesia, were undoubtedly potentiated—if not initiated—by the vasoconstriction due to vasotonins in the circulating blood. The elimination of vasotonins is thought to be the most important technical problem in the improvement of the preparation.