The Body-Machine and Its Work 325 



Sir Arthur Keith describes very graphically the transport 

 of a bolus of food towards the stomach. "The instant that a 

 bolus has been pushed through the doorway leading from the 

 pharynx, and that doorway has closed, we see a ring of con- 

 traction form behind the bolus and commence to creep slowly 

 downwards, forcing the bolus in front of it. The bolus, on enter- 

 ing the oesophagus, has touched a 'button,' and the ring of con- 

 traction is the result. As the bolus is driven forwards it comes 

 in contact with a succession of such buttons, with the result that 

 it is kept moving onwards. Not only so; a ring of relaxation 

 precedes the bolus and eases the passages." * 



The earliest stomach in the animal world was merely a 

 straight tube through which the food passed, but in the course 

 of evolution it has grown larger and larger at this spot until (in 

 man) we have a large storage chamber in which the food will 

 be churned up and mixed with acid and ferment during several 

 hours. The stomach goes up close to the heart on the left side, 

 but its large upper part is less concerned with digestion. The 

 muscular movements which push the food about, so as to expose 

 every part of it to the digestive juices, begin about half-way 

 down the stomach and travel, in waves, towards the bottom. 

 There are three coats of muscle, and they are at work all day 

 long mixing the pulpy contents. The stomach of a healthy and 

 sensible man will get through its work in about four hours, and, 

 if he postpones his next meal, it will, like Oliver Twist, call for 

 more. It develops a peculiar writhing motion in its muscles, 

 and this is telegraphed to the brain by the nerves. You feel 

 "hungry." 



The inner wall of the stomach is richly supplied with blood, 

 and is lined by the myriads of minute glands which produce the 

 "gastric juice." As soon as you sit at table, the sight and smell 

 of the roast mutton send their messages to a certain nerve-centre, 

 and from this a silent message of stimulation goes to the glands. 



>Sir Arthur Keith, The Engineers of the Human Body. 



