Helen: If they are alive, they are. If their bodies are cold, we say they are dead.
Mother: Some birds and animals have more heat in their bodies than we do. The horse has one hundred degrees, the ox one hundred and one, the dog one hundred and two, the sheep one hundred and four, and the duck and pigeon have one hundred and eight. The bodies of some creatures, such as fishes and frogs, are much cooler than our own, and we call them cold-blooded. The frog has only seventy degrees of heat.
Fever thermometer.
Helen: But what makes us warm, mother?
Mother: Do you remember that we talked a good deal about our food as fuel not long ago?
Percy: But, mother, fuel is something to burn, and there is no fire inside of us.
Mother: That is true in one way; but let us see if we can find out where the heat in our bodies comes from. It may be a little hard to understand, but we will try. Here is a candle. If lighted, it burns brightly. Now I will fasten a wire around it and lower it into this glass jar and cover it tightly. Now watch it. What is the matter?
“Now watch it.”