134 PHYSIOLOGICAL CHEMISTRY 



their respective groups. The yolk contains fat and also con- 

 siderable quantities of lecithin and cholesterol. 



Vegetables. Vegetables contain very high amounts of water 

 and thus are low in fuel value. Some vegetables such as peas, 

 beans, and lentils contain only small amounts of water. With 

 the exception of these and a few others, most vegetables contain 

 but small amounts of proteins, very little fat and varying 

 amounts of carbohydrates. As fuel substances therefore most 

 vegetables are far below meats and dairy products. Peas, beans 

 and lentils are exceptions to this statement. Vegetables supply 

 the body with some valuable salts, with some protein, fat and 

 carbohydrate, but they are valuable also from another stand- 

 point. They contain cellulose. Although cellulose is of little 

 food value, it gives bulk to the food, and mechanically irri- 

 tates the walls of the intestines. This stimulates muscular con- 

 tractions which are important for the thorough mixing of the 

 food with the digestive juices, and its transportation along the 

 alimentary canal. The green leafy vegetables such as lettuce, 

 cabbage, spinach, etc., are extremely valuable sources of vita- 

 mines, as will be pointed out later in the discussion of these 

 substances. Fruits also for the most part have little food value, 

 but they are wholesome for the same reason, and they also 

 stimulate the appetite, which is an important factor in proper 

 digestion. Nuts contain much protein, much fat and often con- 

 siderable carbohydrate (peanuts contain protein 25%, fat 38%, 

 carbohydrate 24%) and thus are extremely nutritious. 



Breadstuff's vary greatly in food value. Bread contains about 

 9% protein, very little fat, 53% carbohydrate and 35% water. 

 Its fuel value is about that of average meats, but its protein 

 content is lower. Crackers contain only about 5% water and 

 their fuel value is about double that of bread. Sweet cakes, 

 pastries, etc., usually have a high fuel value. They often are 

 sufficiently indigestible, however, more than to counterbalance 

 their greater fuel content. Some of the breakfast foods are 

 valuable foods but many of them are so light that the amount 

 ordinarily eaten has little total fuel value aside from that of the 



