. The Ontario public school hygiene . mayhave a headache, and you will feel tired and out of sorts. THE BLOOD AND LYMPH 103 In short, strong tea and coffee throw your body out ofgood working order, and though their use has none ofthe degrading effects of alcohol or opium,yet young peopledo not need them and should avoid their use. Youngpeople need to store up strength—not to spend it quickly. CHAPTER XXI THE BLOOD AND THE LYMPH No one needs to be told what blood looks like. Ifa cut in the flesh is large and deep, the blood comesout here and therein jets from a setof tubes, calledarteries. At t
. The Ontario public school hygiene . mayhave a headache, and you will feel tired and out of sorts. THE BLOOD AND LYMPH 103 In short, strong tea and coffee throw your body out ofgood working order, and though their use has none ofthe degrading effects of alcohol or opium,yet young peopledo not need them and should avoid their use. Youngpeople need to store up strength—not to spend it quickly. CHAPTER XXI THE BLOOD AND THE LYMPH No one needs to be told what blood looks like. Ifa cut in the flesh is large and deep, the blood comesout here and therein jets from a setof tubes, calledarteries. At thesame time and fromthe same cut theblood may well upfrom another set oftubes called veins,as water does froma spring. Very soon afterthe cut has beenmade, some of theblood forms a jelly-like mass called aclot, which adheresto the surface of the wound. The use of the clot is tostop bleeding. Loss of blood is so very serious thatNature has been careful to make the blood of all animalsclot very soon after it leaves the Figure 37.—The oval figures with dark centresrepresent the red blood corpuscles hi a frogsblood. These carry oxygen from the lungs allover the body. The round dotted figures repre-sent the white blood corpuscles. These helpto carry food materials to the tissues. 104 PUBLIC SCHOOL HYGIENE Freshly shed blood is composed of a pale straw-coloured liquid called plasma, and floating in this, alarge number of very minute rounded bodies known asblood corpuscles, or blood cells. Of these corpuscles,there are two kinds—red ones and white ones. Thewhite corpuscles and the plasma are the great carriers ofnutritive material. The red take oxygen from the airof the lungs and carry it away in the arteries. Onreaching the very smallest blood-vessels the red cor-puscles deliver the oxygen to the flesh. Here the wetburning occurs about which you have already read. About 90 per cent, of the plasma is water, and, of therest, over 9 per cent, is nutritive material
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