Page:Popular Science Monthly Volume 19.djvu/477

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461
THE BLOOD AND ITS CIRCULATION.

mals chiefly throuarli the lacteals and veins of the stomach: secondly, from the waste of the body received through the lymphatics and thoracic duct; and, thirdly, through respiration, which supplies oxygen. The amount of solid matter seems to bear a proportion to the amount of flesh in the diet and to the temperature of the animal, being greater in the carnivorous and warm-blooded animals.

In color, the blood of all vertebrates is red, excepting that of the

PSM V19 D477 Human blood corpuscles.jpg
Fig. 1.—Human Blood-Corpuscles; magnified 370 diameters.

amphioxus, the lowest animal of the sub-kingdom, which is colorless. In the muscles of fishes it is also white. In the invertebrates the blood is of various colors, but commonly white, on account of which fact they were formerly supposed to be destitute of blood.

Microscopic examination of the blood of a vertebrate animal shows PSM V19 D477 Relative sizes of blood corpuscles.jpgFig. 2.—Blood-Corpuscles (relative size) a, Man; b, Blenny; c, Frog; d, Newt.that the color is due to an immense number of red particles floating in a watery fluid. But the shape and size of these corpuscles vary in the different groups of vertebrates, and in different species. In man, and all mammals excepting the camel tribe, the red corpuscles are biconcave disks. In the camel they are elliptical. The corpuscles in all other vertebrates are nucleated, or have a thickened center. Those of birds, reptiles, and amphibians are elliptical, while those of fishes are discal, elliptical, or angular.

The size of the red blood-corpuscles bears little relation to the size of the animal, except within the natural groups, as the orders of mam-