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The net result of this scheme was that not only did the head and upper 

 extremities receive a hetter quality of hlood, but a right venous and a 

 left arterial heart was maintained and a function was suggested for the 

 Eustachian valve in the right auricle. Unfortunately this doctrine has 

 been antagonized since 1835 with little effect on the described circulation 

 in the mammalian fetus, and with no consideration of its evident defects 

 in the latest text-book (3) on chick embryology. At the last meeting of the 

 Academy I labeled the scheme "morphologically inaccurate, developmentally 

 unnecessary and physically impossible." The second theory (Wolff) was 

 based on excellent anatomical observation but does not fulfil the physical 

 requirements of the proposition. The third theory (Harvey), a mixing of 

 the blood in the right auricle, was quite definitely demonstrated to occur 

 in the living fetal pig. I found by injection experiments that the blood 

 passing into the heart from the right precaval and the postcaval veins 

 found its way into both ventricles. Interpreted in a physiological man- 

 ner, the result is that all the arteries in the mammalian embryo contain 

 a mixed blood. The point raised, while of no practical importance in itself, 

 is interesting because it was first suggested by Harvey in 1628 ; because 

 it may lead to a more perfect understanding of the anatomical changes 

 from the fetal to the adult circulation ; and lastly because of its morpho- 

 logical significance. It is the latter point that I would bring out in greater 

 detail. 



It is well known that the double circulation is found only in the warm- 

 blooded adult vertebrates (bird and mammal) ; animals in other words, 

 where the body temperature demands a greater degree of oxygenation and 

 in which the oxygenation is entirely confined to the lungs. In the lower 

 vertebrates this condition does not obtain, reptiles excepted. The amphibian 

 has other means of obtaining oxygen than through the lungs, and the fish, 

 other paths than through the gills. The relatively low body temperature 

 does not necessitate so rich a content of oxygen in the blood. If we ex- 

 amine this statement closely we see that the embryos of mammal and bird 

 resemble the reptile and amphibian ; they do not possess a distinct four- 

 chambered heart, and while in the latter the element of warmth does not 

 enter, in the former all of the warmth, practically speaking, is supplied 

 by the maternal body through internal or external incubation. The meta- 

 bolic processes of the mammal and bird are therefore insufficient to main- 

 tain the essential body temperature. 



If we examine the phylogenetic relation of the mammal and bird we 



