Breathing with the upper chest is exhausting because of the stiffness of the upper part of the bony cage (see Fig. 75); for it is inclosed by true ribs fixed to the breastbone by short cartilages. The ribs in the waist (Fig. 75) are either floating in front or fixed by long cartilages to the ribs above. In pure abdominal breathing the diaphragm must contract more than in full breathing in order to descend, because its edges have been drawn together and fixed by binding the ribs at the waist. In full breathing the floating and false ribs at the waist (five pairs in all) float in and out as nature provided. As they move out, this broadens and deepens the chest, and aids the flattening of the diaphragm by moving its edges farther apart. Those persons, perhaps one in a thousand, who voluntarily deform the body with tight clothing are beneath contempt. But so uniform is the pressure of tight clothes and shoes that the wearer soon becomes unconscious of them, and so powerful are the effects that not one person in a thousand escapes deformity and injury. Children’s clothing should be supported by the shoulders, and adults’ clothing by both shoulders and hips, but by the waist, never. =Cellular Respiration.=--The chemical activities within the cells and their need of oxygen, not the amount of oxygen in the lungs or blood, determine how much oxygen the cells absorb from the blood. Oxygen cannot be forced even into the blood beyond the required amount. Deep breathing movements, however, help the flow of the blood and lymph. Carried to excess, they tire the will and exhaust the nerves. =Changes in Blood while in the Lungs.=--The coloring matter (or hemoglobin) of the corpuscles absorbs oxygen (and becomes oxy-hemoglobin). Carbon dioxid is given off from the plasma. The blood becomes a brighter red. =Changes in Air in the Lungs.=--The air entering the lungs consists of about one fifth oxygen and four fifths nitrogen. This nitrogen is of no use to the body, and is exhaled unchanged. _A part of the oxygen inspired is taken up by the blood, and carbon dioxid is sent out in its place._ About half a pint of water is given off through the lungs in a day. Minute quantities of injurious animal matter are also given off in the breath from even the soundest person. The air leaves the lungs warmer, damper, and with more carbon dioxid than when it entered (Exps. 3 to 9). [Illustration: FIG. 80.--VENTILATION OF STOVE-HEATED ROOM.[5] How are the inlet and outlet situated with reference to the stove?] [5] From Coleman’s Elements of Physiology (400 pp.). The Macmillan Co., N.Y.