Ask the students to name some ways of staying cool in summer. They may mention going into the shade, or sitting under a fan. Discuss with them how the body itself has mechanisms to keep cool. Let them feel the air which they breathe out. Is it cool or warm? Let them hold a loose fist to the mouth and blow in and out through it. They will immediately feel the difference in temperature of the air passing in and out. Explain how this is one way in which the body stays cool. Make the students run fast. When they stop, they will start panting. The reason for panting is that the body has generated a lot of heat and needs to cool faster.
Explain how perspiration is another method by which the human body stays cool. Let them lick the back of their hand and blow on it. That part of the skin will feel cool. Explain that evaporation does a similar thing.
VARIATION / EXTENSION
Ask them to say how common domestic animals keep themselves cool. Talk about the buffalo which needs to lie in water for several hours or the dog which keeps panting with its tongue hanging out. If references are available, you may like to discuss how wild animals keep themselves cool. 
