What are the indications that Schatz is ill, and what does he think is the matter with himself in the story "A Day's Wait"?

Schatz is pale, he shivers, and he has a fever with symptoms of influenza; but because he mistakenly interprets his temperature in Celsius degrees, he believes he is going to die.

After a shivering Schatz awakens and comes into his parents' room to shut their windows because he feels the draft, Papa notices that he looks ill. He tells Schatz to return to his room; in the meantime, the father dresses and descends to the main part of the house only to find Schatz already dressed and sitting by the fireplace, appearing miserable. Placing his hand on his son's forehead reveals to the father that Schatz has a fever, so he summons the doctor.

Outside the boy's room, the doctor tells the father that Schatz's fever is 102 degrees, and there is no need to worry unless it rises to above 104. He also provides the father with three medications, one of which is designed to lower the fever. After the doctor departs, the father returns to the boy's bedroom and offers to read to him. But Schatz seems "very detached from what was going on," and he is pale with dark areas under his eyes. Without his father's knowing it, Schatz has overheard the doctor say his temperature is 102, and because he goes to school in France, he has heard from other boys that "you can't live with [a temperature] of forty-four." Therefore, Schatz thinks he is going to die.

Since he thinks he will not live, he tells his father, 

"You don't have to stay in here with me, Papa, if it bothers you."
"It doesn't bother me."
"No, I mean you don't have to stay if it's going to bother you."

Misunderstanding Schatz's meaning, the father simply assumes that his son is light-headed from the fever and the medication that he gives him. He leaves to go hunting, hoping the boy will sleep quietly while he is gone. However, when the father returns, he is told that Schatz has forbidden everyone from entering his room so that no one will catch his illness. He approaches Schatz and discerns that the boy is yet pale, "staring still as he had stared at the foot of the bed." He takes the boy's temperature, and it has lowered to around 100. "It was 102," Schatz says. The father asks him how he knows this because he has not realized that his conversation with the physician was overheard. Schatz replies, "The doctor."

His father tries to reassure Schatz that his temperature is nothing to worry about, but Schatz seems to be "holding tight onto something." Finally, Schatz asks, "About what time do you think I'm going to die?" The father is astounded by this question, and he asks his son, "What's the matter with you?" The boy insists that he is going to die because the students at school have told him that "you can't live with forty-four degrees. I've got a hundred and two." Then the father realizes that poor Schatz believed that his temperature was in Celsius when he overheard the doctor. He explains to his son the difference between Celsius and Fahrenheit and reassures him that he will be all right. However, although the boy's hold over himself relaxes, the next day poor Schatz cries easily at little things as a backlash to his previous self-control.