“The what?” asked the little corpuscle.
“The gate toll. Be quick; you are keeping others waiting.”
“But what is this toll, and what is it for?”
“An atom of oxygen. It is to pay me, to be sure, for maintaining this valve that prevents you from being forced back into the heart.”
“But,” persisted the corpuscle, “I must be sent along. Why should I pay you when I am doing the work of the organism and shall pay it before I get through? If I cannot get through the whole organism will suffer.”
“Hurry up, hurry up, there is no time to talk,” said the valve, and as the crowd was impatiently pushing behind him the little corpuscle gave up an atom of oxygen and hurried on.
“You must pay me an atom too,” murmured a voice in his ear.
“Who are you?” asked the corpuscle.
“I am the aorta. You will have to pay me for carrying you to the general circulation.”
“But if I pay you I shall have to rob the tissues that need what I am carrying, and it will be impossible to procure from them what I need to keep me alive in turn. I must get my load along.”