192 THE ENGINES OF THE HUMAN BODY 



which give the pulse-beat, took place at a rate of between 

 72 and 80 a minute. How is the rate of the contractions 

 regulated in the heart ? The stomach, as we have already- 

 seen, has also a pulse — one which beats at from 3 to 5 

 times a minute. In the heart the wave of contraction in 

 the ventricle is so quick that to our eye it appears to 

 involve the whole chamber at once. Careful measurement, 

 however, shows that there is really a wave which spreads 

 over the ventricle — much as a train of gunpowder is fired 

 when a match is applied to it. In the stomach contraction 

 waves spread slowly and in one direction ; we can see 

 them very distinctly because they are not hurried. Now, 

 in the heart we know that the contraction waves arise at 

 one point — a nodal point — just as an exploding train of 

 gunpowder spreads from an ignition point or percussion 

 cap. Nodal points seem to serve as percussion caps for 

 starting waves of contraction. There is in the muscular 

 coat of the stomach, near the oesophageal opening, a patch 

 of tissue which serves as a nodal point for starting the 

 contraction waves of the stomach. These become visible 

 and marked when they reach the pyloric part of the 

 stomach. They are produced slowly, only 3 to 5 a 

 minute. Thus the stomach, as well as the heart, has a 

 regular beat or pulse, and so, we shall find, have the other 

 parts of the alimentary tract. 



Nature in her contrivances has considered not only 

 our daily needs but has extended them to the exigencies 

 which arise from abnormal or disordered conditions. She 

 has elaborated a nerve centre or control exchange which, 

 on the receipt of messages of distress, can actually empty 

 the stomach. The vomiting centre can take charge of the 

 musculature of the stomach and not only reverse its action 

 but also bring into use all the muscles of the body which 

 are accessory to the act of vomiting — the diaphragm, the 

 muscles- of the oesophagus and throat, — and thus by a 

 combined effort empty the stomach of its contents. 



The vomiting centre is accessible to messages from 

 nearly all parts of the body. They may arise from the 

 womb, from any part of the bowel, stomach, or throat. 



