Circulation      

    A teacher was giving a lesson on the circulation of the blood.  Trying to make the matter clearer, he said:  “Now, boys, if I stood on my head the blood, as you know, would run into it, and I should turn red in the face.”

    “Yes, sir,” the boys said.

    “Then why is it that while I am standing upright in the ordinary position the blood doesn’t run into my feet?”

    A little fellow shouted, “’Cause yer feet ain’t empty!”

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