Popular Science Monthly/Volume 19/September 1881/The Blood and Its Circulation II > 자유게시판

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By HERMAN L. FAIRCHILD. IN vertebrates alone is there a closed circulation-an entire system of tubes from whence the blood by no means escapes into the body-cavity. We discover an approach to it in the upper mollusks. Indeed, in energy and common effectivity, the circulation of the very best mollusks is tremendously superior to that of the low vertebrates. Nevertheless, the completely closed circulatory system of even the bottom vertebrates is of higher type. Although the circulating system of the vertebrates is perfected in precept, it still admits of very great and curious modifications. There exist in vertebrates three sets of capillary blood-vessels, which are normally spoken of as three programs, although collectively they represent but a single circuit. They are distinguished because the body or BloodVitals systemic circulation, the respiratory or pulmonary circulation, BloodVitals and the liver or portal circulation. Connected with the blood-system by the thoracic duct is the lymphatic circulation. The lymphatic system, which has beforehand been mentioned because the second supply of blood materials, deserves some discover on account of its intimate relation with the blood system of the vertebrates.

The lymphatics are minute capillary vessels, Blood Vitals present in all components of the physique of vertebrates, BloodVitals monitor excepting, maybe, the bulb of the eye, BloodVitals experience the cartilages, and BloodVitals the bones. The office of the lymphatics is to collect the waste matter of the tissues and return it to the blood, BloodVitals to be again used elsewhere, or, if wholly ineffective, to be excreted from the body. Additionally they accumulate the blood which may be poured upon the tissues in excess of their needs. The fluid which the lymphatics carry is known as lymph. It is colorless, and monitor oxygen saturation comprises corpuscles resembling the white corpuscles of the blood. The lacteals, which take the brand new food from the intestines, are lymphatics modified for a special goal, BloodVitals health and, when they aren't busy with the chyle, in addition they carry lymph. The lymphatic tubes are provided with valves to keep the lymph flowing toward the bigger trunks. This lymphatic system of the vertebrated animals is, nevertheless, expressed in technical language, solely the differentiated interstitial sinuses of the lower animals, BloodVitals which has, within the latter, a share within the Fig. 1. Diagram of the Circulation in a Fish.

Indeed, within the lower vertebrates the lymphatic tubes ceaselessly assume the form of giant sinuses, and connect with the veins. They're even discovered within the birds. Within the frog 4 of those sinuses have muscular partitions, and rhythmically contract. These are often called lymphatic hearts. In numerous components of the physique the lymphatics kind glands, such because the thymus, thyroid gland, and the spleen. Fishes have a heart resembling that of the mollusks. It's a double drive-pump, consisting of a receiving-chamber (auricle), and a propelling chamber (ventricle), with all the valves crucial to prevent a backward circulation of the blood. But this heart is respiratory-it sends the blood on to the breathing organs; consequently, it passes only impure blood. When the blood has traversed the gills and is purified, it passes around the circuit of the body by the systemic and portal capillaries, and back to the center with none additional propulsion. The low, worm-like fish, lancelet, or BloodVitals amphioxus, has no special coronary heart, but a variety of contractile bulbs within the veins.

The eel has such an auxiliary coronary heart in its tail, while the hag has the circulation aided by the contractility of the portal vein. Lepidosiren, one of the mud-fishes, approaches the amphibians within the possession of two auricles; for, along with gills, it has true lungs. The vein conveying the purified blood from the lungs joins the left auricle. Amphibians and reptiles exist beneath circumstances incompatible with a excessive temperature of the physique. Within the grownup state they're air-breathers, and, if their circulation have been full, they can be "heat-blooded." However the temperature is subdued by imperfect circulation, which outcomes from the arrangement of the guts-chambers. There may be but one ventricle for the 2 auricles, therefore the pure blood from the respiratory organs and the impure blood from the body are mingled, in order that, besides the venous and arterial, they've a combined blood. The blood which goes to the lungs isn't wholly impure, and that which works to the physique is never completely pure.