CONSTITUENTS OF PLANTS 377 



ability of the food, and perhaps exert a favorable influence upon 

 digestion by stimulating the secretion and flow of the digestive 

 juices. 



Essential Oils. The characteristic flavor and odor of many 

 plant products are due to volatile compounds known as essential 

 oils. Turpentine, peppermint oil, oil of roses, and oil of lemon 

 are examples of essential oils. Spices, flavoring extracts, condi- 

 ments and appetizers in general, flowers, and certain fruits are 

 characterized for the most part by the presence of essential oils. 

 Hays owe a portion of their odor and flavor to essential oils. 

 Rape, turnips, cabbage, and parsley contain essential oils. Some 

 of the essential oils impart palatability to the food, and stimulate 

 the secretion and flow of the digestive juices. While 

 of little or no value for the production of muscle or energy, they 

 aid the appetite of the animal. 



Certain feeds containing essential oils are undesirable for milch 

 cows, as they impart a disagreeable flavor to the milk. Garlic, 

 wild onions, and rape are examples of these. 



Organic Phosphorus Compounds. Plants also contain organic 

 phosphorus compounds, chief among which is phytin, 1 which may 

 be decomposed into inosite and phosphoric acid. This substance 

 is found especially in wheat bran, rice bran, and cottonseed meal. 

 Other organic phosphorus compounds are present. 



Heat Value. The energy of a feed or nutrient is measured by 

 the heat which it produces when burned. The unit of heat is the 

 calorie, written c., which is the amount of heat required to raise 

 the temperature of I gram water i Centigrade. The large 

 calorie (C) is 1,000 c, and the therm (T) is 1,000 C. Several 

 kinds of calorimeters are used. In the bomb calorimeter, the 

 material is placed in a platinum capsule in an iron vessel, lined 

 with platinum or enamel. The bomb is filled with oxygen under 

 high pressure, and placed in a vessel of water with a stirrer, and 

 thermometer, and properly insulated to decrease heat changes. 

 The material is ignited by means of an electric current which 

 heats a small piece of iron wire, and the rise in temperature of 

 the water is ascertained. Knowing the amount of heat required to 

 1 N. Y. (Geneva) Bull. 250; Texas Bull. 156. 

 25 



