A TRANSPORT SYSTEM 173 



meantime we return to watch a single bolus of bismuth- 

 laden food propelled along the first stage of its journey, 

 from the pharynx to the stomach. The model in whom 

 we are to watch its transit by the help of X-rays is a man 

 of medium but spare build ; in him the bolus has to be 

 carried a distance of 12 inches, 2 J of which lie in the 

 pharynx, 9^ in the gullet or oesophagus. Even although 

 we are watching closely when the bolus is shot by the 

 piston-like action of the tongue into the pharynx, the 

 exact nature of the first part of the act is so quick that 

 we cannot be sure of what has taken place ; but presently 

 we see in the neck, behind the windpipe, the black 

 shadow of the bolus set out at an almost snail-like pace, 

 making about 2 inches per second. Then by turning our 

 model round, so that we may look obliquely across the 

 chest, we again detect the black shadow creeping slowly 

 down in front of the backbone until the level of the 

 diaphragm is reached. There it seems to hesitate and 

 stop two, three, or more seconds, as if knocking at the 

 door of the stomach for entrance. As a matter of fact 

 it is knocking, according to the custom recognised along 

 the alimentary canal ; it is waiting for the lock-gates to 

 open which allow it to trickle or creep into the stomach 

 some eight or nine seconds from the time it leaves the 

 mouth. Were there no muscular sphincter or lock-gates 

 at the gullet or cardiac opening of the stomach, then every 

 time we take a deep breath, or press upon the epigastrium, 

 or stoop down to lift an object from the ground, our 

 meals would be forced from the stomach towards the 

 mouth. When the bolus enters the stomach, the cardiac 

 doorway is again closed. 



The transit of a bolus of food from the pharynx to 

 the stomach, whether we watch it by X-rays or trust 

 to our daily experience, seems so easy and expeditious 

 that we are surprised, when we look at the construction 

 of the pharynx and oesophagus, by the complexity of the 

 machinery which has to be set in motion. We have seen 

 (fig. 33, p. 135) that the pharynx is a busy crossing used 

 by two streams of traffic — air traffic and food traffic. 



