158 THE ENGINES OF THE HUMAN BODY 



thus permitting our bodies to become overcooled. Heat 

 can escape from the body much more easily on a damp day 

 than on a dry one. Dr Hill has also drawn attention to 

 the demands made on the heat-producing system by cold, 

 biting, damp winds. Such a wind pierces our clothes and 

 sweeps from their meshes the curtain of warm air main- 

 tained there by the body heat. No sooner is one curtain 

 gone than the body starts to build up another layer of 

 hot air, which is swept away in turn by the blast which 

 follows. And so the heat supply of the body is steadily 

 drained to keep up the surrounding curtain of warm air. 

 Now it is just at such times that disease-producing germs 

 may gain an advantage, unless our heat-producing and 

 heat-regulating mechanisms are perfectly sound. Such a 

 drain on our heat supply stimulates the vitality of the 

 sound body, but it lowers the powers of resistance of the 

 body which has been weakened, so that the heat-producing 

 mechanism does not respond to vagaries in the weather. 

 It is under such conditions that the micro-organisms 

 which cause " colds " — everyone has them lurking some- 

 where in his breath passages^ — make a successful attempt 

 to invade the living systems of the human machine. 



