198 THE ENGINES OF THE HUMAN BODY 



in the intestine, then, is the manufacture and production 

 of this starch-reducing substance. The nitrogen-contain- 

 ing elements in the chyme have also to be dealt with. 

 The nature of the change worked by the intestine on 

 them can best be made clear by the use of an illustration. 

 We take wool from the sheep and make it into clothing 

 for our own bodies. When the cloth has become worn 

 we may weave it again, but before that is possible we 

 must tear the cloth to fine shreds — reduce it to the con- 

 dition of shoddy — before it can again go to the loom. 

 That is what the intestine has to do with the albuminous 

 articles of our diet. They are composed of huge complex 

 molecules built up in the living bodies of animals and to 

 a less degree in the seeds of plants. The intestines have to 

 split up these great molecules — reduce them to " shoddy " 

 so that they may again be woven into the texture of the 

 living tissues. We saw that the process of reduction or 

 digestion was commenced in the stomach ; it is continued 

 and carried to a further extent in the intestinal factory. 

 The bowel is a shoddy mill, but the means employed are 

 chemical. Nature again uses one of her miraculous 

 wedges — a ferment or enzyme named trypsin. The manu- 

 facture of trypsin is another industry carried on in the 

 bowel. Then there is a third important element of our 

 diet — fats. Everyone is aware that fat forms the basis of 

 soap and that soap can be dissolved in water. The 

 intestines convert fat to form a soap by the use of a 

 special ferment or enzyme — lipase. The manufacture of 

 lipase is another industry carried on in the intestine. By 

 the use of these enzymes the raw materials of our food 

 are reduced to a condition which makes them suitable to 

 be used as body-fuel. 



The juice which contains these digestive enzymes is 

 formed from the blood by living microscopic units. 

 Along the whole length of the bowel these units are 

 grouped so as to form minute test-tubes which are 

 packed closely together side by side, with their mouths 

 opening on the surface of the lining membrane. The 

 lining membrane, in which the test-tubes are set, is per- 



