197.WHAT CAUSES A REFLEX?
When you go to the doctor, does he ask you to cross your legs and then hit your knee with a small rubber hammer?
What the doctor is testing is the reflex action. In this case, it is a special reflex called the patellar reflex, because the hammer struck a ligament called the patellar ligament.
196.WHAT ARE OUR TEETH MADE OF?
Do you brush your teeth at least twice a day? If you do, and you brush hard, have you ever wondered why you don’t wear your teeth down? The fact is that our teeth are pretty tough—about as hard as rocks. Every tooth is made up of the same two parts: a root, or roots, to anchor it in the jaw bone, and a crown, the part that can be seen in the mouth.
195.WHAT ARE OUR BONES MADE OF?
The strength of normal, healthy human bones is amazing. The saying that our bones are “twice as strong as oak” is not far from wrong.
Bone needs to be strong because it forms the framework, or skeleton, that supports the whole body. Bones vary in shape and size according to the type of animal to which they belong. Fish and small birds have tiny bones. Elephants have bones that weigh several hundred pounds!
