. The bird, its form and function . particle of bad blood can get through and vitiate thelife-giving stream which has just come from the lungs. A Bluebird is perched on a twig near its nest mur-muring its sweet warble; a Wood Pewee, half hiddenin the shadows of some dense, moist forest, speaks tous in its sad dreamy phrase; how calmly, how quietlythey sit! It seems impossible to believe that every dropof blood in their bodies is rushing back and forth withinconceivable rapidity—from heart to head, from bodyto wings and legs, and back again! Let us take the blood as it is just leaving the heart
. The bird, its form and function . particle of bad blood can get through and vitiate thelife-giving stream which has just come from the lungs. A Bluebird is perched on a twig near its nest mur-muring its sweet warble; a Wood Pewee, half hiddenin the shadows of some dense, moist forest, speaks tous in its sad dreamy phrase; how calmly, how quietlythey sit! It seems impossible to believe that every dropof blood in their bodies is rushing back and forth withinconceivable rapidity—from heart to head, from bodyto wings and legs, and back again! Let us take the blood as it is just leaving the heartin the breast in one of these little feathered beings, andtrace its course through the body and back again tothe starting-point. The left ventricle opens into theaorta, the greatest artery, or blood-tube leading fromthe heart, in the body. The clean oxygen-food-bearingstream rushes through this channel, which we may com-pare to the trunk of a tree, and is carried into brancharteries, dividing finer and finer, just as the trunk of. Fig. 135.—Circulatory system of Pigeon (injected), showing blood-vessels rami-fying from the heart to every part of the body. i 84 The Bird the tree merges into limbs, and these into branches, twigs,stems, and at last into the delicate foliage. This lastwe may liken to the capillaries or hair-tubes in whichthe blood does its real work of supplying nourishmentdirectly to the tissues, and where it receives the wastematters, carrying them away in its current. When we have followed the divisions of a tree outto the foliage, we may find that they touch and interlacewith the foliage of another tree, and this is very muchlike what occurs in the course of the blood. The capil-laries run together and form larger vessels, these in turncoalesce, and soon the blood—dark now and filled withthe waste matters of the body-cells—is flowing throughonly two large veins (veins always lead toward the heart).These enter the right auricle, which opens into the right
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbirds, bookyear1906
