sour salty biller sweetin these areas containnerve endings whichrespond strongly to a particular
taste. All taste sensationsotherthan sweet, sour, bitter and salty are caused
by acombinationofodorand taste.
OBSERVING ABEEF HEART
Materials:Ask yourbutcherfor theheartof a steer (beef). Besides this,
all you need is asharpknife. Be surethatyou have permission to use the knife.
Follow this procedure:Cut the beefheartdown the centerlongitudinally
(the long way) sothatyou can see its four chambersand thebloodvessels
leading from thebroadend, or top, of the heart.
You will observe:The beefheartis a thickmuscularorganwith cut ends
ofbloodvesselsconnectedto theupperpart. Like theheartsofall animals
in thegroupto which man belongs(mammals),the beefhearthas fourseparate
chambers. The two smallerupperchambersare calledauricles,and the two
lowerchambersare calledventricles.
The left sideoftheheartis clearly separatedfrom the right side. The
upperchamberofthe right side is connected to the lower right chamberby
a valve (asortof"trapdoor"). Theupperleft side isconnectedto the lower
left side by a similar valve.
Notice, too,thatthe lowerhalfof theheartis thicker and moremuscular
thantheupperpartandthattubes, the cut endsofblood vessels, all seem to
come from theupperpartofthe heart.
The beefheartis typical of the heartsofallmammals,a classofanimals
which includes man. Theheartsofallmammalsare divided into fourchambers.
Theheartacts as apump,receiving blood which it then pumps outtovarious
partsofthe bodythroughblood vessels.
The top rightchamber,the right auricle, receives blood from allpartsof
the body. The blood which flows into the right auricle has been used; thatis,
it hasalreadyfunctionedin food digestion and inprovidingfresh oxygen for