"Good morning, Sir," replied the students.
"How was your vacation?" he asked.
"It was very good, Sir. We threw lots of snowballs and made a snowman!"
"So, you enjoyed the snow over the week-end, then" he smiled at the class.
"Yes, teacher, we had lots of fun," they answered.
The teacher looked around the classroom and frowned. "I see that some a couple of students haven't come to school today."
"Yes, Saleem and Aisha are not here today."
"Do you know why?"
"They stayed home, Sir," the class said. "They must be sick."
"That means they must have played in the snow too long," frowned the teacher.
"We played in the snow too; will we get sick, teacher?" asked the class, alarmed.
"If you aren't careful and stay out in the snow too long, you may do."
"Why does snow make people sick? We love it when it snows. And we like playing in it."
The teacher explained: "The reason people get sick is that germs have entered their body. As you know, germs are invisible organisms. They enter our bodies and try to do us harm. If we're not careful about hygiene, and eat without washing our hands, they can get into our body and stay there."
"Will we get sick right away after germs enter our body, Sir?" the students wanted to know.
"No," he replied. "We don't always get sick. When Allah created us He gave our bodies a wonderful immune system to fight germs. We don't realize it, but the elements of this immune system protect our bodies just like an army. Every element of this highly complex immune system does its duty perfectly."
"So, Sir, why do we get sick? Is it because our immune system has not done its duty?"
"No, in a normal person, the immune system is always working. Without our knowing it, our immune system is engaged in a big war against germs. First of all, it tries to prevent germs from entering and remaining in our bodies. If germs do manage to enter our bodies it destroys them immediately."
"Why do we get sick, then?" they still wanted to know.
"If we stay out in the cold too long," he explained, "And if we are careless about eating our meals, our bodies lose strength. When this happens, our immune system gets weaker too. The germs that haven't been destroyed multiply and spread quickly throughout our bodies."
"So, when this happens, do the germs take over our whole bodies?" they asked.
"No," he continued. "In that case, our immune system starts an even bigger war against the germs. Because of this big war that is going in on our bodies, we get a fever, we feel out of sorts and our joints begin to ache."
The students nodded. "Yes. When that happens we have to stay in bed."
"Of course, when that happens the best thing we can do is rest. If we get plenty of rest and take medicine at the same time, and if we eat all our food, our immune system will get stronger and help us. So, in a short time it will defeat the germs and throw them out of our bodies. In this way, we become healthy again."
"Now we understand how we get sick," the students told him. "From now on, we will be very careful."
"Yes," the teacher said: "Allah gave us a great blessing when He created our bodies and such a defense system in it. We should thank Him very much for it, and look after ourselves so that we don't lose the health that He gave us."
They said "Glory be to You!