Identifier: courseinbiobailfirstrich (find matches)
Title: First course in biology
Year: 1908 (1900s)
Authors: Bailey, L. H. (Liberty Hyde), 1858-1954 Coleman, Walter Moore, 1863-1926
Subjects: Biology
Publisher: New York : The Macmillan Company
Contributing Library: University of California Libraries
Digitizing Sponsor: MSN

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large, firm, and of a darker red; by disuse, it be-comes small, flabby, and pale. But if muscles are workedtoo constantly, especially in youth, their cells do not havetime to assimilate food and oxygen, and their growth isstunted. Unless the meal has been a very light one, vigorousexercise should not be taken after eating, as the blood willbe drawn from the food tube to the muscles and the secre-tion of the digestive fluids will be hindered. Personswhose entire circulation is weak may find that light exerciseafter a meal, such as walking slowly, may help circulationand digestion. Why the Muscles work in Harmony. — When a boy throwsa stone, almost every part of the body is concerned in theaction. His arms, his legs, his eyes, the breathing, thebeating of the heart, are all modified to assist in the effort. Illustrated Study of Muscular Function Draw a dotted line from each function mentioned on margin to the muscleor muscles having that function. Bows the head? \ Draws shoulder back?
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arm outward arm downward elbow ? Bends the fingers? Raises the body on the Raises toes? Fig. 44. —Superficial Muscles after the Statue of The Digger (Lami). 43 44 HUMAN BIOLOGY As the boy wills to throw the stone, nerve impulses aresent to all the organs that can assist, and they are excitedto just the amount of action needed. The Nerve Impulse and the Contraction. — Each nervethat goes to a muscle is composed of many fibers; thefibers soon separate and go to all parts of the muscle,and each muscle fiber receives its nerve fiber (see Fig. 45). In the brain each fiber isstimulated at once, and allthe fibers shorten and thickentogether. This change isspoken of as contraction ; butsince the muscle does not be-come smaller, the word maybe misleading. When themuscle shortens, it thickensin proportion and occupies asmuch space as it did whenrelaxed. Where does Muscular En-ergy come from?—The nervedoes not furnish the energywhich the muscle uses whencontracting. The muscle cellshave al

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