328 The Outline of Science 



the chemical message, and sets more vigorously to work pour- 

 ing an increased supply of digestive juice into the intestine. 

 These marvellous messages which are, as it were, posted in the 

 blood are called "hormones," and, as we shall see later on, we 

 find them again and again accounting for very remarkable results 

 in the body. 



The liver and the pancreas are really outgrowths from the 

 alimentary tube; sections which have become detached, special 

 departments, with ducts leading to the bowel. Each pours about 

 a pint of fluid daily into the bowel, to assist the work of digestion. 

 The liver has very special work to do, and we shall notice it 

 presently. Here we need only say that the bile which it pours 

 into the bowel sometimes so abundantly that some forces its 

 way into the stomach, and you get "bilious" is not a digestive 

 juice, but it helps to prepare the fats in the food. The pancreatic 

 juice, on the other hand, is a real digestive juice, and the starches 

 and sugars and fats, as well as the nitrogenous foods, are now 

 dissolved and made into emulsion, and prepared, in short, for 

 absorption. The juices of the pancreas and of the intestine 

 include powerful ferments, or enzymes. These are substances 

 which cause chemical changes by their mere presence, without 

 being used up in bringing about these changes. One of them 

 deals with the starches and sugars in the food, another with the 

 fats, another with the proteins, like white of egg. 



The chyme the pulped and semi-digested food moves 

 slowly along the bowel. In the bowel wall are muscles which 

 contract, and drive the contents slowly onward at about one 

 inch a second. But the interior wall of the tube is now lined, 

 not only with glands, but with little outstanding fingers, like (on 

 a microscopic scale) the pile on fine velvet. The surface is, 

 moreover, puckered into folds, to give a larger area, and myriads 

 of the tiny fingers or villi dip into the chyme and absorb the 

 nourishing matter. Altogether about sixteen square feet of 

 absorbing surface are given in the small intestine, and it is there 



