324 The Outline of Science 



pharynx to pass unchecked." Food does not "go down," as chil- 

 dren think. The whole mouth changes. Certain sensitive spots 

 at the back of the mouth electrical press-buttons, we may call 

 them give the signal that the food is ready. The powerful 

 muscles which closed the back of the mouth while we are masti- 

 cating, relax. The lower jaw is pressed against the upper. The 

 soft palate forms an inclined plane. Other muscles close the air- 

 ways to the nose and the great airways to the lungs. The whole 

 complex machine acts together and pumps the food into the first 

 part of the alimentary tube, the pharynx. Only very rarely does 

 a little food "go the wrong way"- into the air-passage and then 

 another set of muscles automatically blow (or cough) it out. 

 The mouth is a rather complicated cavity. How many communi- 

 cations it has with the nasal passage by the posterior nostrils, 

 with the ear-passages by the Eustachian tubes, with the pharynx, 

 and with the windpipe through the guarded glottis. It is obvi- 

 ously very important that the mouth be kept in good order. 



The food now enters upon a very long journey. Most people 

 are surprised to hear that the alimentary tube is yards long in 

 a man or woman of medium height, about twenty-eight feet long 

 from the mouth to the vent. But few people reflect there would 

 be far less misery and discomfort in the world if they did what 

 digestion really means. Our food has to be broken up, physically 

 and chemically, and even then it cannot pass into the blood. 

 From the pulpy mass myriads of tiny organs have to select the 

 matter which the body needs, and let the remainder pass away. 

 So the food has to pass slowly through twenty feet of a long 

 tube, the small bowel or small intestine, to give these "selectors" 

 the chance of taking the nourishment from it. 



However, let us begin at the beginning. The food passes 

 to the stomach down a one-foot tube (in a man of medium 

 height), the upper part of which is known as the pharynx, and 

 the lower part as the gullet or oesophagus. As we said, it does 

 not slide down. 



