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It is not necessary we should argue the point as to whether oxygen displaces carbonic acid in the tissues proper or the capillaries. The theory of Lavoisier on this point has been accepted.
But modern science has proved that it is in the capillaries that animal heat is generated, and it is believed that alcohol lessens instead of increasing the power of the body to bear the cold. Sir John Koss, in his Arctic voyage, proved by his own experience and that of his men that cold-water drinkers could bear cold longer and were stronger than any who used alcohol.
It needs all the impulsive power of the heart to enable the blood to force its way through these narrow passages; and minute as are the globules, it would seem that they have but just room to pass, for in examining under the microscope a corner of the tongue of a live frog, the globules have been seen doubling themselves up to pass through the capillaries, resuming their natural form afterwards.
After meandering through the capillaries at c, to distribute oxygen and food from the stomach, the blood enters the vein, b, loaded with carbonic acid and water taken up in the capillaries, to be carried to the lungs or skin, and thrown out into the air. The manner in which the exercise of the muscles quickens the circulation of the blood will now be explained.
The surface of the body no longer suffices to gather oxygen, hence we find special feathery gills on the parapodia. But these gills are merely expanded portions of the body wall, arranged so as to offer the greatest possible amount of surface where the capillaries of the blood system can be almost immediately in contact with the surrounding water.
Raynaud suggested that the local syncope was produced by contraction of the vessels; the asphyxia is probably caused by a dilatation of the capillaries and venules, with persistence of the spasm of the arterioles.
But, as already suggested, it has certain movements which are necessary to the purposes which it serves. A careful study shows it to have three well-defined movements as follows: 1. A movement from the capillaries toward the cells. A movement from the cells toward the capillaries.
All the blood flows continuously through both circulations and passes the various parts in the following order: right auricle, tricuspid valve, right ventricle, right semilunar valve, pulmonary artery and its branches, capillaries of the lungs, pulmonary veins, left auricle, mitral valve, left ventricle, left semilunar valve, aorta and its branches, systemic capillaries, the smaller veins, superior and inferior venæ cavæ, and then again into the right auricle.
*Functions of the Capillaries.*—On account of the thinness of their walls, the capillaries are able to serve a twofold purpose in the body: 1. They admit materials into the blood vessels. They allow materials to pass from the blood vessels to the surrounding tissues.
#Aneurysm by Anastomosis# is the name applied to a vascular tumour in which the arteries, veins, and capillaries are all involved. It is met with chiefly on the upper part of the trunk, the neck, and the scalp. It tends gradually to increase in size, and may, after many years, attain an enormous size. The tumour is ill-defined, and varies in consistence.
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