CHAPTER IV - THE BLOOD
Two liquids of similar nature are found in the body, known as the blood and the lymph. These are closely related in function and together they form the nutrient fluid referred to in the preceding chapter. The blood is the more familiar of the two liquids, and the one which can best be considered at this time.
The Blood: where Found.—The blood occupies and moves through a system of closed tubes, known as the blood vessels. By means of these vessels the blood is made to circulate through all parts of the body, but from them it does not escape under normal conditions. Though provisions exist whereby liquid materials may both enter and leave the blood stream, it is only when the blood vessels are cut or broken that the blood, as blood, is able to escape from its inclosures.
Physical Properties of the Blood.—Experiments such as those described at the close of this chapter reveal the more important physical properties of the blood. It may be shown to be heavier and denser than water; to have a faint odor and a slightly salty taste; to have a bright red color when it contains oxygen and a dark red color when oxygen is absent; and to undergo, when exposed to certain conditions, a change called coagulation. These properties are all accounted for through the different materials that enter into the formation of the blood.
Fig. 8—Blood corpuscles, highly magnified. A. Red corpuscles as they appear in diluted blood. B. Arrangement of red corpuscles in rows between which are white corpuscles, as may be seen in undiluted blood. C. Red corpuscles much enlarged to show the form.
[pg 025]Composition of the Blood.—To the naked eye the blood appears as a thick but simple liquid; but when examined with a compound microscope, it is seen to be complex in nature, consisting of at least two distinct portions. One of these is a clear, transparent liquid; while the other is made up of many small, round bodies that float in the liquid. The liquid portion of the blood is called the plasma; the small bodies are known as corpuscles. Two varieties of corpuscles are described—the red corpuscles and the white corpuscles (Fig. 8). Other round particles, smaller than the corpuscles, may also be seen under favorable conditions. These latter are known as blood platelets.
Red Corpuscles.—The red corpuscles are classed as cells, although, as found in the blood of man and the other mammals (Fig. 9), they have no nuclei.[6] Each one consists of a little mass of protoplasm, called the stroma, which contains a substance having a red color, known as hemoglobin. The shape of the red corpuscle is that of a circular disk with concave sides. It has a width of about 1/3200 of an inch (7.9 microns[7]) and a thickness of[pg 026] about 1/13000 of an inch (1.9 microns). The red corpuscles are exceedingly numerous, there being as many as five millions in a small drop (one cubic millimeter) of healthy blood. But the number varies somewhat and is greatly diminished during certain forms of disease.