190 THE ENGINES OF THE HUMAN BODY 



minute mouths of the test-tube glands — the microscopic 

 retorts — which form the gastric juice. Through the 

 living pavement the absorbed elements have to pass 

 before they reach the capillary blood-field which occupies 

 the spaces between the test-tube glands. It is not a mere 

 physical process of diffusion ; the pavement units have a 

 taste of their own ; gastric juice they reject, some fluids 

 may lie in the stomach for hours and yet they will not 

 touch them. Having passed the pavement barrier, the 

 absorbed products are then really within the machine — 

 if not a living part of it. In the blood they are carried 

 straight to the greatest chemical factory of the body — the 

 liver. There they undergo further preparation and also 

 storage. 



Having thus glanced at the chemical changes undergone 

 by the food in the stomach, we return to consider a few 

 of the more remarkable contrivances connected with the 

 regulation of its transport system. We have already 

 seen that the pyloric gateway is guarded by a sphincter 

 and that it played the part of a cautious janitor in regu- 

 lating the rate at which the contents of the stomach were 

 discharged into the duodenum. If there were no janitor 

 at the pylorus, the stomach would empty itself within 

 a quarter of an hour or less of being filled, and thus throw 

 the burden of its work upon factories further down the 

 line already burdened with as much work on hand as they 

 can overtake. When we look at the circular muscular 

 coat of the stomach (fig. 40) as it passes on towards the 

 pyloric gateway we see that it gradually becomes thicker, 

 and then, when it actually reaches the pylorus, it rapidly 

 increases to a great thickness, and at the same time its 

 manner of action alters. The pyloric sphincter is always 

 in a state of action or contraction ; the gateway is always 

 shut. Then, beyond the pylorus, the circular muscular 

 coat, as it passes on to the duodenum, becomes very thin 

 and reassumes a normal state — one of relaxation. We 

 notice that when the contraction waves which milk the 

 contents of the stomach towards the gateway actually 

 reach the sphincter, they cease ; they do not spread into 



