. Animal biology; Human biology. Parts II & III of First course in biology. Biology. 46 HUMAN BIOLOGY food, g ives a good appetite, and sets the digestive organs to work; it uses up the oxygen and sets the lungs to work ; but most of all, every contraction of a muscle helps the blood to flow. As a muscle contracts, it presses upon the veins and lymphatics, and, by this pressure, forces the blood and lymph along (Fig. 48). In any ordinary activity, dozens of mus- cles are being used. That the effect upon the circulation is very pow- erful, is shown by the rosy skin, deep breath- ing, and ra
. Animal biology; Human biology. Parts II & III of First course in biology. Biology. 46 HUMAN BIOLOGY food, g ives a good appetite, and sets the digestive organs to work; it uses up the oxygen and sets the lungs to work ; but most of all, every contraction of a muscle helps the blood to flow. As a muscle contracts, it presses upon the veins and lymphatics, and, by this pressure, forces the blood and lymph along (Fig. 48). In any ordinary activity, dozens of mus- cles are being used. That the effect upon the circulation is very pow- erful, is shown by the rosy skin, deep breath- ing, and rapid heart beat. The many benefits of an active circulation of the blood and lymph will be discussed in the next chapter See page 67. A grave danger from athletics is that of developing the muscles, including the heart, to an enormous extent by training; then ivhen training ceases the muscles undergo fatty degeneration from disuse. Heart disease and other diseases may follow. Many athletes die young, killed by trying to turn their bodies into mere machines for run- ning, boxing, or rowing, instead of living complete lives. The athletic ideal is not the highest ideal of health ; gen- eral activity, resembling the occupations of hunting and farming by which the early race supported itself, is best for health. Many kinds of factory work use only one set of muscles. The savage did not lead a monoto- nous life, and monotony is bad for both muscles and FIG. 48. — CAPILLARIES among fibers of voluntary (cross striped) muscle. (Peabody.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bailey, L. H. (Liberty Hyde), 1858-1954. New York, The Macmillan Co.
Size: 1587px × 1574px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectbiology, bookyear1910
