The Human Mechanism

ers, eyes, teeth, tongue, and other organs. But we do not often realize that the work of each organ is equally the resultant of the work of its component cells. Eyes, hands, and tongue we can see and even watch at their work, but the cells of muscles and glands and nerves are invisible. If we could see them and delve into their recesses, we should there discover activities no less remarkable. As we cannot do this directly and with the naked eye we must do it indirectly and make use of experiments, chemical analyses, microscopic studies, and all other available methods. And we may again choose for detailed consideration two typical organs, muscle and gland, the structure of which we have studied in the last chapter. 1. Physiology of the Salivary Glands. Working Glands and Resting Glands. ? The function of the salivary glands is the secretion or manufacture of saliva for use in the mouth, and one of the first things we notice about this act of secretion is that it is not constant but intermittent. Most organs have periods of activity, or lvork, followed by periods of inactivity, or rest, and these glands are no exception. Physiologists frequently speak of " working glands "and " resting glands." We all know that our own salivary glands work more effectively at some times than at others. The mouth " waters " at the sight of food; when we are in the dentist,s chair the flow of saliva often seems excessive; and at other times our mouths are "parched" or " dry." 2...