Experimental studies on the circulatory system of the late chick embryo.

A method of preparing the 15/17-day chick embryo for physiological studies is described and the results of an investigation of flow patterns in the circulatory system using oxygen determinations and dye injections is reported. A considerable separation of deoxygenated and oxygenated blood streams occurs in the incompletely divided heart such that a large part of the oxygenated stream flows through the perforated interatrial septum to the left heart for distribution to head, neck, thorax and heart. A mechanism also exists whereby the gut and yolk sac receive blood at an oxygen saturation greater than the remainder of the posterior body. Some quantitative estimates of blood and oxygen flows are made and the circulatory system of the late chick embryo is compared with that of the foetal mammal.