"How long have I been sick?" she asked one morning.
"It is four weeks yesterday," said Papa.
"Four weeks!" said Katy. "Why, I didn't know it was so long as that. Was I very sick, Papa?"
"Very, dear. But you are a great deal better now."
"How did I hurt me when I tumbled out of the swing?" asked Katy, who was in an unusually wakeful mood.
"I don't believe I could make you understand, dear."
"But try, Papa!"
"Well—did you know that you had a long bone down your back, called a spine?"
"I thought that was a disease," said Katy. "Clover said that Cousin Helen had the spine!"
"No—the spine is a bone. It is made up of a row of smaller bones—or knobs—and in the middle of it is a sort of rope of nerves called the spinal cord. Nerves, you know, are the things we feel with. Well, this spinal cord is rolled up for safe keeping in a soft wrapping, called membrane. When you fell out of the swing, you struck against one of these knobs, and bruised the membrane inside, and the nerve inflamed, and gave you a fever in the back. Do you see?"