Elementary anatomy, physiology and hygiene for higher grammar grades . thing disturbs, startles,or irritates them, they instantly fold the bells in, draw the 36 PHYSIOLOGY cilia together, and contract the stem until they occnpythe smallest possible space. This all shows that they are sensitive, and thatthey can respond to astimulus. Remember that allcells begin as smallyoung cells and growup to adult life by eat-ing; that all cells haveto work for their living;that all cells breathe inoxygen and breathe outcarbon dioxide gas; thatall cells are sensitive tothipgs or conditions out- FiG. 11. — A
Elementary anatomy, physiology and hygiene for higher grammar grades . thing disturbs, startles,or irritates them, they instantly fold the bells in, draw the 36 PHYSIOLOGY cilia together, and contract the stem until they occnpythe smallest possible space. This all shows that they are sensitive, and thatthey can respond to astimulus. Remember that allcells begin as smallyoung cells and growup to adult life by eat-ing; that all cells haveto work for their living;that all cells breathe inoxygen and breathe outcarbon dioxide gas; thatall cells are sensitive tothipgs or conditions out- FiG. 11. — A Stentor {a, b) and a Vorticella • t j^ ,i -i j (c,d). a and c show these little one-celled Siae 01 tnemseives ; ana animals relaxed, with the hell open, and that many Cells have the the little hairs around the mouth ol the . bell waving the particles oi food into the pOWCr 01 motion. open mouth of the bell. 6 and c show Remember that many both animals contracted after something i ? i has startled them. [Verworn.] plants and animais Con- sist of only one 4. TISSUES —HOW THEY ARE MADE AND WHATTHEY DO If you will turn back to Figure 7 and Figure 10, youwill see that full-grown plant cells and full-grown animalcells divide into two or more young cells which begin lifeas small, restless, hungry cells which forage for food, eatravenously, and grow rapidly into adult cells. In theamoeba the daughter cells separate, and each one goes offby itself where it must fight its own battles single handed. CELLS, TISSUES, AND ORGANS 37
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