268 SCIENCE REMAKING THE WORLD 



There are also foods which were originally despised 

 because of their poor showing in the respects referred to 

 above, which are now valued for another cause. The 

 normal activity of our digestion demands a certain 

 bulk to our food mixture, even though that bulk is se- 

 cured by materials which are classed as indigestible. 

 It is of course obvious that no matter how rich a food 

 may be in the qualities outlined above, the nutrients 

 must be of such a nature that the digestive juices can 

 act upon them and so change them that they will pass 

 freely from the digestive organs to the blood. If not 

 they will fail to reach the muscle, nerve, skin, bone, and 

 other structures they are intended to nourish. This 

 property, then, demands that our foods be digestible, 

 but if we attempted to feed a man on completely digesti- 

 ble mixtures his stomach and intestines would in time 

 become atrophied. In other words we must have pres- 

 ent a certain amount of indigestible matter to provide 

 bulk and stimulation to the lining of the digestive tract. 

 The cellulose which forms the coating of starch grains, 

 the connective tissue that forms the indigestible portions 

 of meats, etc., are examples of such substances. We 

 speak of them as roughage and they are mechanical 

 necessities of our food mixtures which must not be 

 neglected if we are to avoid constipation and like ills. 

 In general, then, while our foods must contain digestible 

 nutrients they should also carry a certain amount of 

 indigestible roughage. 



Finally the form of the food offered is important. 

 Eating is to a high extent a psychological affair. If 

 the food is presented in an unpalatable form the body 



