NUTRITION 121 



at all digested in the intestine of man, but stimulates the 

 peristaltic movements, probably by mechanical stimulation 

 of the intestinal muscles. This causes vegetables to pass 

 through the intestine more rapidly than animal food. The 

 food of the vegetables is inclosed in cellulose coats and 

 hence is not directly accessible to the digestive fluids. By 

 preparing the vegetable foods (grinding, cooking, baking) 

 the cellulose envelopes are burst and the food proper can 

 then be readily acted upon by the digestive fluids. 



As a food the vegetable proteid is of equal value to the 

 animal proteid. The carbohydrates of vegetables are gen- 

 erally present in the form of starch, and, to a smaller 

 extent, as sugar (dextrose, fructose, cane-sugar, maltose). 

 Starch is rendered more digestible by boiling, which causes 

 it to swell. 



Grinding changes the grain foods to fine particles flour. From 

 this the cellulose envelopes (bran) are removed by sifting. The 

 more bran the flour contains, the richer it becomes in proteid, for 

 the richest proteid layer of the grain lies just below the cellulose 

 envelope. The flour is used in baking bread, etc. The baking 

 is made possible by a proteid, called gluten. The leaven (yeast) 

 added to the dough, produces carbon dioxide by its sugar fermen- 

 tation which loosens the bread. In many kinds of bread (black 

 bread, graham bread), flour rich in bran is used, and the cellulose 

 of the bran aids the peristalsis of the intestine and prevents con- 

 stipation. 



The leguminoses are peculiar because of their large amount of 

 proteid. They contain no gluten and can therefore not be used 

 in baking. They contain, however, a proteid called legumin 

 which forms, when boiled with lime water, an insoluble compound 

 with calcium. Hence they must always be boiled in soft water 

 (containing no lime), otherwise they remain hard. 



To obtain nourishment from such foods as greens, cabbage, 

 lettuce, fruits, which are rich in water, a large quantity must be 

 taken. They are therefore not used as a principal food but only 

 as supplemental to others, and serve as condiments because of 

 their flavors. They also furnish the cellulose necessary for the 

 peristalsis. 



As to the question whether animal food or plant food is 

 more suitable for man, it may be stated that a mixed diet 

 consisting of one-third animal and two-thirds vegetable food 



