'.r
THE HUMAN HEART AND PULSE
Materials:A stop watch or a watch with a secondhand,paperand pencil.
Forthis experimentyou will need acompanion,either aparentor a friend.
Follow this procedure: Withthe first two fingers(notthethumb)of your
righthand,hold the left wrist of yourcompanion. Search for the pulse until
you feel it and can counteachdistinctbeat. Record the numberof pulse
beats perminutewhileyourcompanionis in eachofthe followingsituations:
lying down, at rest,
sitting in a chair
standing
afterjumpingup and down in place to thecountof 20
afterrunningup and back down a flight of stairs.
You will observe:The pulsebeatis slowest when apersonis lying down,
and fastest after he has run up and down stairs.The pulsethatyou felt when you heldyourcompanion'sleft wrist repre-
sents the beats of hisheart. Heartbeats are thecontractionsof the thick, left
ventricle muscles of theheartas it directsbloodto allpartsofthe body.
When the bodyis at rest, it requires relatively little nourishment and
oxygen; therefore, the heart beats relatively slowly. It beats rapidly (as
indicated by anaccelerated pulse) when the body requiresenergy for such
activities asrunningup and down stairs.MAKING AWORKING MODEL OF THE CHEST CAVITY
Materials:A belljar(a glass vessel open at the bottomand bell-shaped
atthe top), a Y-shapedglass tube, a pieceofrubbersheeting largeenoughto
cover the open end of the belljar,twoidenticalrubberballoons,several elastic
bands,a woodenbutton,eithera rubberstopperor acorkwith a holethroughit.
Follow this procedure: Insertthe tail ofthe Y-shapedtube in the cork
orstopper. With an elasticband,attacha balloonto each"Y"projectionof
the glass tube.
Now, insertthestopperor cork, with theY-shapedtubeattached,in the
neck of the belljar. Place rubbersheeting across thebroadend of the bell
jarand secure with arubberband.
To make thismechanicalbreathingapparatusresemble the activity of the
humanchest,pinchthe middle of therubbersheeting withyourthumband
forefinger and gently pull itdownward. Thenslowly release the sheeting and
watch itreturnto itsoriginalposition.