Anatomy, physiology and hygiene . rease in capability,and then to reproduce. Living things are also excitable, they — each in its own peculiar manner — respondto external impressions, such as cold, heat, a blow, ornervous force. These excitants are spoken of as cells when stimulated secrete, others excrete, whilein others the protoplasm alters its form. Certain cellsin our bodies, like some of the one-cell forms of animallife, have the power of moving from place to place bythe alternate protrusion and retraction of various por-tions of their protoplasm. Movements of this sort
Anatomy, physiology and hygiene . rease in capability,and then to reproduce. Living things are also excitable, they — each in its own peculiar manner — respondto external impressions, such as cold, heat, a blow, ornervous force. These excitants are spoken of as cells when stimulated secrete, others excrete, whilein others the protoplasm alters its form. Certain cellsin our bodies, like some of the one-cell forms of animallife, have the power of moving from place to place bythe alternate protrusion and retraction of various por-tions of their protoplasm. Movements of this sort arecalled amoeboid movements, since they resemble thoseof the amoeba. They enable the lymph cells and thewhite blood cells to pass, through the thin walls of thevessels in which they float, into surrounding tissues. THE HUMAN BODY. GENERAL FACTS. 9 Such migration is known as diapedesis,1 and the cellsengaged in it are emigrant or migratory cells. Diseasesometimes spreads from one tissue to another by means ofthese cells. 0 e?. Fig. Movements. Another form of motion inherent in certain cells is theciliary^ the waving to and fro by means of ciliae. Mus-cular motion, through the alternate contraction and relax-ation of muscular fibres, is also a property possessed bymany living things. 9. Membranes. —Fibrous, sheet-like tissues, which covercertain organs and connect certain parts of the body, arecalled membranes. Some membranes, placed as partitionsbetween two fluids or gases, permit them to mingle. Thisprocess is known as osmosis. The passage of the fluidor gas inward is endosmosis; outward, exosmosis. Theabsorption of a fluid by a cell or membrane is is illustrated in the changes which occur in thebreathed air during respiration* imbibition, in the trans-formation of food into blood. 1 Greek, 5ia, through, itvidav, to 10 THE HUMAN BODY. GENERAL FACTS. 10. The Tissues. — The tissues of the body may 1:classified as supporting tissues an
Size: 1877px × 1332px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjecthealth, booksubjectph
