Lessons in elementary physiology / Thomas H. Huxley.

  • Huxley, Thomas Henry, 1825-1895.
Date:
1888
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Licence: Public Domain Mark

Credit: Lessons in elementary physiology / Thomas H. Huxley. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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    carbonic acid, but whose hcemoglobin also has lost a great deal of its oxygen, would be purple. 6. Now all the tissues, as we have seen, are continually using up oxygen. Their life in fact is dependent on a continual succession of oxidations. Hence they are greedy of oxygen, while at the same time they are continually producing carbonic acid (and other waste products). Thus, as the blood is flowing through the capillaries of a tissue we have on the one side of the permeable capillary wall the blood with its corpuscles rich in oxygen, and on the other ,side the tissue in constant want of oxygen, and constantly producing a large quantity of carbonic acid. The result is that the oxygen flies from the red corpuscles through the capillary wall to the tissue, which at once takes it up, while the carbonic acid passes from the tissue where it is in excess through the capillary wall to the blood which, though containing carbonic acid, does not hold so much as the tissue. The blood therefore leaves the tissue poorer in oxygen and richer in carbonic acid than when it came to it ; and this change is the change from the arterial to the venous condition. On the other hand, if we seek for the explanation of the conversion of the dark blood in the veins into the scarlet blood of the arteries, we find, ist, that the blood remains dark in the right auricle, the right ventricle, and the pulmonary artery ; and, -that it is scarlet not only in the aorta, but in the left ventricle, the left auricle, and the pulmonary veins. Obviously, then, the change from venous to arterial takes place in the pulmonary capillaries, for these are the sole channels of communication between the pulmonary arteries and the pulmonary veins. 7. But what are the physical conditions to which the blood is exposed in the pulmonary capillaries ? These vessels are very wide, thin walled, and closely set, so as to form a network with very small meshes, which is contained in the substance of an extremely thin mem- brane. This membrane is in contact with the air, so that the blood in each .capillary of the lung is s_eparated from the air by only a delicate pellicle formed by its own wall and thje lung membrane. Hence an exchange vejy readily takes place between the bipod and the air ; the latter G