They increase respiration, and thus increase the life-giving oxygen and animal heat, while they repress excess in other congested parts.
They increase nutrition, and also the secretion and discharge of morbid matter from diseased or weakened parts.
CHAPTER VIII.
DOMESTIC EXERCISE.
In a work which aims to influence women to train the young to honor domestic labor and to seek healthful exercise in home pursuits, there is special reason for explaining the construction of the muscles and their connection with the nerves, these being the chief organs of motion.
The muscles, as seen by the naked eye, consist of very fine fibres or strings, bound up in smooth, silky casings of thin membrane. But each of these visible fibres or strings the microscope shows to be made up of still finer strings, numbering from five to eight hundred in each fibre. And each of these microscopic fibres is a series or chain of elastic cells, which are so minute that one hundred thousand would scarcely cover a capital O on this page.
Fig. 49 Fig. 50.
The peculiar property of the cells which compose the muscles is their elasticity, no other cells of the body having this property. At Fig. 49 is a diagram representing a microscopic muscular fibre, in which the cells are relaxed, as in the natural state of rest. But when the muscle contracts, each of its numberless cells in all its small fibres becomes widened, making each fibre of the muscle shorter and thicker, as at Fig. 50. This explains the cause of the swelling out of muscles when they act.
Every motion in every part of the body has a special muscle to produce it, and many have other muscles to restore the part moved to its natural state. The muscles that move or bend any part are called flexors, and those that restore the natural position are called extensors.