. The human body and health : an elementary text-book of essential anatomy, applied physiology and practical hygiene for schools . ssues are more quiet, and therefore requirelittle oxygen, while during exercise the muscles are con-suming oxygen rapidly, and it can be supplied frcgn thelungs only. When the tissues need oxygen, a messageis sent to the cells of the spinal cord, which orders themuscles of the chest used in breathing to work faster. Respiration. — Passing air in and out of the lungs iswrongly called respiration. True respiration is of twokinds : the external or hlood respiration oc
. The human body and health : an elementary text-book of essential anatomy, applied physiology and practical hygiene for schools . ssues are more quiet, and therefore requirelittle oxygen, while during exercise the muscles are con-suming oxygen rapidly, and it can be supplied frcgn thelungs only. When the tissues need oxygen, a messageis sent to the cells of the spinal cord, which orders themuscles of the chest used in breathing to work faster. Respiration. — Passing air in and out of the lungs iswrongly called respiration. True respiration is of twokinds : the external or hlood respiration occurs in thelungs, while internal or tissue respiration takes place in thetissues all over the body. Blood respiration consists inthe passage of oxygen from the air cells into the bloodand of the carbon dioxide from the blood into the air air received into the lungs contains in every 10,000parts 1 parts of carbon dioxide, 2096 parts of oxygen,and 7900 parts of nitrogen. When it issues from thelungs, there are 438 parts of carbon dioxide, 1602 parts ofoxygen, and 7900 parts of nitrogen. THE CAPACITY OF THE LUNGS 141. Tissue respiration consists in the giving up of theoxygen of tlie blood to the cells of the tissues, and the receiving of tlie carbon dioxide from the tissuesinto the blood. Nocell can do its workwithout a constantsupply of oxygen, andin doing its work someuf the oxygen mustunite with the carbonto form carbon dioxide. The Capacity of theLungs. — In ordinarybreathing, only one pintof air passes in and outof the lungs. This iscalled the tidal air. Inaddition to this threepints of air may bebreathed in by effort. This is eomj)lemental air. Afterthe ordinary expiration about three pints of air, namedthe supplemental air, may by effort be forced out, butthere will still remain some air in the lungs. This isresidual air. The vital capacity of the lungs is thequantity of air that can be breathed out by the deepestexpiration after the deepest inspiration. The us
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