A NOTE ON AN ABNORMAL XENOPUS LAEVIS SPECIMEN WITHOUT HAEMOGLOBIN and on some~eriments performed as a consequence.

In the blood vascular system of a typical fish, the blood is sent from the heart to the gills for oxygenation and thence to the rest of the tissues, before returning once more to the heart. This is a so-called "Single Circulation". Where lungs make their appearance in the vertebrate series however, their blood supply is derived from the last of the aortic arches and is returned via the newly formed pulmonary veins, directly to the heart. A part of the blood leaving from the heart is sent to the lungs, and a part to the rest of the body tissues. Two circuits are formed, both of which have the heart as a central point, and a "Double Circulation" is thus established. In post-embryonic birds and mammals, where metabolism is highest, these two circuits are separated by the development of a complete septal division in the heart, in such a way that all of the blood returning from the body tissues is first passed to the lungs for re-oxygenation. After this has occurred, it is returned to the heart so that it may receive sufficient propulsion for its journey to the body. The intervening series of vertebrates, between these extremes (including the embryonic stages of birds and mammals, where the lungs are non-functional), have various degrees of anatomical division in the heart structure of the different classes. Up to some twenty years ago, it was generally accepted that, in spite of the imperfect separation of the two sides of the heart in these classes, some physiological "attempt" was made by the animal to approach the perfect double circulation. Relatively little experimental work has been done to·test this idea. The anuran Amphibia present a somewhat unusual case, - 2 - in that the division of the heart is complete in the atrium, but incomplete elsewhere. The ventricle has no septal division at all and there is only a partial division of the bulbus cordis by a spiral valve. There appears to be less anatomical division therefore, in the Anura, than in the dipneumone Dipnoi or any· of the reptiles. Even Neoceratodus possesses a septum in the ventricle. Another peculiar feature of the Amphibia as a whole, is an accentuated form of cutaneous respiration, which introduces an undetermined, but presumably large, proportion of oxygen into the blood stream returning from the body tissues. This seems an argument against the necessity of a division in the heart, at least if such a division is related to the distribution of oxygenation and de-oxygenated blood to the body and lungs respectively. In view of the complication introduced by these peculiarities, the Anura do not seem to form logical subjects upon which to start an experimental investigation of the vertebrates with incompletely divided hearts. It appears to bethese very idiosyncrasies however, which have stimulated a small number of physiologists. The problems involved, have been brought into prominence particularly by Vandervael (1933) and Faxon (1947, 1951, 1955), both of whom have presented evidence against the idea of a separation of blood streams in the anuran heart. Nevertheless it is most surprising, considering the importance of frogs and toads as laboratory animals, that more attention has not been directed towards the functioning of their central circulatory apparatus. This "complacency", so to speak, has probably been the outcome of the superficially satisfying account, now generally known as the "classical theory". The present investigations were carried out in the hope that they might add some information towards the understanding of the subject, as least in so far as one additional 3 - species, Xenopus laevis, is concerned.