. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 276 RESPIRATION. blood is poured into the pulmonary system at the left side of the respiratory rete. The cur- rent, therefore, entering the left auricle is not pure arterial blood : it is alloyed by the venous rivulet received from the bronchial system, — a reptilian characteristic traceable in human organisation. By a third class of observers it is said, that the capillaries of the pulmonary and those of the bronchial system of vessels intimately inosculate. The precise solution of this question is difficult, in consequ
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 276 RESPIRATION. blood is poured into the pulmonary system at the left side of the respiratory rete. The cur- rent, therefore, entering the left auricle is not pure arterial blood : it is alloyed by the venous rivulet received from the bronchial system, — a reptilian characteristic traceable in human organisation. By a third class of observers it is said, that the capillaries of the pulmonary and those of the bronchial system of vessels intimately inosculate. The precise solution of this question is difficult, in consequence of the readiness with which an injection thrown into one vessel will pass into another by extrava- sation. Other anatomists suppose that the three above-described modes of communica- tion actually exist. It is certain that these two systems do communicate, and that only a part of the blood of the bronchial arteries re- turns by the bronchial veins. More recently, a new aspect has been given to this controversy by the statements of Dr. Heale, to the effect that the bronchial and the pulmonary systems of vessels do not in any manner or degree communicate. He maintains, on the evidence afforded by his injections, that the vascular web of the air-cells extends, and is prolonged over the internal surfaces of the bronchial tubes. Dr. Heale assigns to this extension cf the rete mirabilc the power of prolonging the aeration of the blood. This is impossible. The bronchial tubes, the minutest, are inter- nally lined by a dense ciliated epithelium. Such epithelium does not exist on the true capillary parts of the lungs of any vertebrated animal. Where there is ciliated epithelium, a universal principle of structure requires in the higher vertebrated animals that the function of breathing should be suppressed. This prin- ciple, however, does not obtain in respiratory organs of the invertebrata, and in the bron- chial organs of lower vertebrata. Respiratory Organs of Birds. The lung
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