PREPARATION OF TISSUE-FUEL 187 



pathways for messages passing from the stomach to the 

 nerve centres as well as from these exchange centres to 

 the stomach. Messages are being constantly dispatched 

 and received, particularly at meal-times. 



Then there are its lymphatic vessels or lacteals, channels 

 of a kind which are found in every organ, although this 

 is the first reference which has been made to them. The 

 tissues of the human machine are provided, as are the 

 inhabitants of a modern town, with a sewage system. 

 The refuse which escapes from the living units of the body 

 tissues is gathered and carried away by special channels or 

 vessels. Those of the stomach and bowel are named 

 lacteals, because during digestion they carry a milk-like 

 fluid called chyle, while in other parts of the body the 

 fluid conveyed by them is transparent like water and 

 therefore named lymph. The tissue sewage contains 

 substances which can be again utilised in the body, and it 

 is, therefore, not rejected from the system but poured by 

 the thoracic ducts into the great veins as these approach 

 the heart. 



Although the stomach has all the outward appearance 

 of being simply a soft-walled double-mouthed bag, yet 

 when we look more closely it turns out, in reality, to be a 

 great chemical factory. Food, the raw material from which 

 tissue-fuel is prepared, occupies its great chamber ; into 

 its wall are built not only the miniature retorts which are 

 to furnish the solution or juice needed for chemical treat- 

 ment of the food, but also myriads of microscopic engines 

 which bring the retorts in contact with the food, and sub- 

 sequently discharge such contents as are fit to be passed 

 on to the next factory — the duodenum. When we begin 

 a meal, even before food has actually reached the stomach, 

 the miniature retorts all over the inner wall begin to 

 manufacture and pour out a juice or solution that exer- 

 cises a digestive action on the food exposed to it. The 

 mechanism which sets secretion going is not of the 

 " touch-button " kind, for food applied directly to the 

 lining membrane of the stomach does not excite the flow 

 of gastric juice. The nerve exchange which controls the 



