II. OF WHAT CELLS ARE MADE 10 III. DIGESTION OF FOOD IN THE MOUTH 13 IV. DIGESTION OF FOOD IN THE STOMACH 17 V. FOODS 23 VI. TOBACCO 31 VII. FERMENTATION 37 VIII. KINDS OF STRONG DRINK 42 IX. THE BLOOD 49 X. BREATHING, HEAT, AND CLOTHING 59 XI. THE SKIN AND KIDNEYS 75 XII. THE NERVES, SPINAL CORD, AND BRAIN 84 XIII. THE SENSES 100 XIV. BONES AND JOINTS 109 XV. MUSCLES 115 XVI. DISEASE GERMS 123 XVII. PREVENTING SICKNESS 132 INDEX 139 APPLIED PHYSIOLOGY CHAPTER I CELLS Our body is made of many parts. Its head thinks. Its legs carry it, and its arms and hands take hold of things. The leg cannot do the work of the arm, nor the head do the work of the hand; but each part does only its own work. =1. The simplest animal.=--Some animals have parts like a man's; but these parts are fewer. No animal has arms or hands like a man. A fish has little fins in place of legs and arms, while a worm has not even a head, but only a body, and yet it moves. An oyster has only a body and cannot move. The simplest of all animals is very small. A thousand of them would not reach an inch. Yet each is a complete animal. It is called the _ameba_. It is only a lump of jelly. It can put out any part of its body like an arm and take a lump of food. This same arm can eat the food, too. It can also put out any part of its body like a leg and move by rolling the rest of its body into the leg. It can do some things better than a man can do them, for any part of its body can do all kinds of work. So the ameba grows and moves and does as it likes. [Illustration: =Different forms of an ameba (×400).=] [Illustration: =Cells from the human body (×200).= _a_ A colored cell from the eye. _b_ A white blood cell. _c_ A connective tissue cell. _d_ A cell from the lining of the mouth. _e_ Liver cells. _f_ A muscle cell from the intestine.] =2. Cells.=--A man's finger moves and grows something like a separate animal, but it must keep with the rest of the body. A little piece of a finger moves and grows, too. If you should look at a finger, or any other part of your body, through a microscope, you would see that it is composed of little lumps of jelly. Each little lump looks like an ameba. We call each lump a cell. The cells make up the finger.