PREPARATION OF TISSUE-FUEL 183 



same moment. In people with active digestions a con- 

 traction wave will appear every ten seconds, giving the 

 stomach a beat or pulse of six to the minute, but three 

 to the minute is quite a common rate. Clearly we are 

 watching the transport system of the stomach at work — 

 the system employed for passing food on from one to 

 another of the chemical factories lying along the alimentary 

 system. 



When we observe what happens to the shadows of the 

 contraction waves as they approach the pyloric gateway, 

 we see that many of them become dissipated there and 

 seem to have produced no other effect than mixing and 

 pulping that part of the meal which is contained in the 

 lower tubular or pyloric part of the stomach. But every 

 now and again a wave is successful in forcing a little of 

 the more fluid part of the pyloric contents into the third 

 chemical factory of the alimentary system — the duodenum ; 

 after a successful wave we can make out a spray-like 

 shadow formed by the ejected bismuth-laden material in 

 the first part of the duodenum (fig. 39). Indeed very 

 soon after the test meal reached the stomach these small, 

 broken-up duodenal shadows began to appear, showing 

 that the stomach begins almost immediately to discharge 

 the more fluid parts of a meal. A glass of water taken 

 before breakfast will, if the stomach is working as in 

 health, be discharged into the duodenum within ten 

 minutes or less from its being swallowed. 



While these wave-like movements are in progress in 

 the lower tubular part of the stomach, pulping and lique- 

 fying its contents, nothing is to be seen of them in the 

 upper or main chamber. We may regard the upper part 

 as a hopper or retort from which the lower or grinding 

 part is fed. We notice, too, that the discharge from the 

 pyloric part becomes accelerated after an hour or two ; 

 presently the shadow presented by the stomach becomes 

 confined to its tubular part. By 12 a.m. — in four hours 

 from breakfast-time — the whole of the meal will have 

 been discharged if the stomach is working as in health. 



The rate of discharge depends on a number of circum- 



