Investigations Into the Distribution of Blood in the Heart and Aortic Arches of Xenopus Laevis (Daud.)

Abstract

The structure of the heart of Xenopus laevis is described, and the differences between Xenopus and Rana are stressed. 2. A fluorescein-cinematographic method of tracing blood flow and an optical manometer for the measurement of blood pressure in Xenopus are described. 3. The right atrial blood is absorbed into the trabecular meshwork only on the right side of the ventricle. 4. Whereas the output of the right atrium is not, or only in negligible quantities, transferred to the left side of the ventricle, a considerable proportion of the output of the left atrium moves to the right half of the ventricle. 5. The left atrium has a larger output than the right atrium. 6. Almost all the blood expelled from the right atrium is sent to the pulmo-cutaneous arches. 7. The blood from the left atrium is distributed to all the arterial arches and the pulmo-cutaneous arches receive a considerable proportion of this blood. 8. More blood flows through the pulmo-cutaneous arches at each beat than is sent through the carotid and systemic arches together. 9. The rate of flow in the pulmonary circuit is much higher than that in the body circuit. 10. A physiological connexion is demonstrated between the left side of the ventricle and the systemic and carotid arches, and between the right side of the ventricle and the pulmo-cutaneous arches. 11. Pressures in the pulmo-cutaneous arch are consistently lower than in either the carotid or systemic arches. 12. The pressures in the carotid and systemic arches are remarkably similar. There is, therefore, no sound reason for postulating a mechanism in the carotid labyrinths which should maintain a higher pressure in the carotids than in the systemics. 13. The pulse curves in the arches show two waves: the first, major, one produced by contraction of the ventricle, the second one by contraction of the bulbus cordis. 14. The spiral valve may not come into contact with the opposite wall of the bulbus before contraction of the latter. Before that time, i.e. as long as the major propulsive force of the ventricular contraction is not expended, the cavum pulmo-cutaneum is in open communication with the ventricle. 15. The pulmonary veins show a weak pulse, and their pressure is higher than in the hepatic veins. This indicates smaller resistance in the pulmonary circuit than in the body circuit. 16. The selective distribution is neither in agreement with the ‘classical theory’ nor with ideas of random distribution. 17. The forces underlying the selective distribution and the significance of the pattern are discussed.