NUTRITIVE VALUE OP FEEDING STUFFS 37 



of animal products, like meat, fat, milk, eggs, etc., which will later 

 supply energy to man or other animals when used in their feed. 



The burning of a material in a stove and the oxidation of the 

 digested nutrients in the animal body are similar chemical processes, 

 differing mainly in the intensity with which they run their course. - 

 In either case, organic substances unite with the oxygen of the 

 air or blood, and form carbon-dioxide and water (also urea in the 

 case of protein substances oxidized in the body ) . The same amount 

 of heat is given off whether the oxidation takes place in or outside of 

 the body. The heat evolved on combustion is a measure of the 

 chemical energy stored up in the feeding stuff that may be used 

 by animals for the repair of the body tissue, for the formation 

 of body fat or muscle, and incidentally for maintaining the body 

 heat. The general law of the conservation of energy governs the 

 transformation of chemical energy into heat and work in the animal 

 body, as it does outside the body. They are manifestations! of the 

 same force, and all energy supplied in the food will eventually re- 

 appear and be accounted for in the form of heat or work, or as the 

 chemical energy of meat, fat, etc., stored in the body. The fact 

 that the law of the conservation of energy* applies to the changes 

 taking place in the animal ibody has been fully demonstrated by 

 scientists in this country and abroad through experiments with man 

 and various animals; in this country especially by Atwater and 

 Benedict experimenting with man, and by Armsby and his co- 

 workers in experiments with cattle. 



Various units have been employed for measuring the heat of 

 combustion. The common unit is a Calorie, which represents the 

 amount of heat required to raise the temperature of one kilo- 

 gram of water one degree Centigrade, or that of a pound of water 

 very nearly four degrees Fahrenheit. A therm, as. proposed by 

 Armsby, means 1000 Calories, the amount of heat required to raise 

 the temperature of 1000 kilograms (2204.6 pounds) of water one 

 degree Centigrade. This unit has been generally adopted of late 

 years and will be used in the following pages. 



The various components of feeding -stuffs contain certain 

 amounts of oxygen and are, therefore, partially oxidized. Carbo- 

 hydrates thus contain about 50 per cent of oxygen, fats 10 to 12 per 

 cent, protein 22 per cent (pp. 9, 13, 14). The amount of heat 

 evolved in the combustion of any organic material depends on the 

 proportion of oxygen it requires for complete oxidation of the car- 

 bon, hydrogen, nitrogen, and other chemical elements contained 

 therein. This amount can be calculated in the case of sub- 

 stances of known composition, and directly determined in a so- 

 called calorimeter. 



