THE BALANCE OF NUTRITION 2IQ 



energy either as to form or intensity, and this fact has led some 

 physicists to identify the concepts of matter and energy and to 

 maintain that the former can be fully interpreted in terms of 

 the latter. Without entering here into this debated question, 

 it will be convenient to follow for our present purpose the more 

 familiar course of regarding matter and energy as two distinct 

 although indissolubly connected entities. 



306. The conservation of energy. When a unit of kinetic 

 energy is converted into heat energy it is found that the amount 

 of heat obtained is always the same no matter what the process 

 employed in effecting the conversion. Similarly, if a unit of 

 heat be converted into kinetic energy the amount of the latter 

 obtained is always the same and moreover is always equal to 

 the quantity of kinetic energy which disappears when one unit 

 of heat is produced. 



What is true of heat energy and kinetic energy in this respect 

 has been shown to be true of all the forms of energy. Not only 

 are they convertible into each other but there is no loss or gain 

 of energy in the conversion. When a quantity of energy of one 

 form disappears an equivalent quantity simultaneously appears 

 somewhere in some other form or forms. This great generali- 

 zation, perhaps the most important in the history of physical 

 science, is known as the law of the conservation of energy, or 

 the first law of energetics. It was first clearly and distinctly 

 formulated by Mayer in 1842 and since that time has been 

 verified by a great number of the most exact experiments and 

 forms the basis of modern conceptions of physical processes. 

 In substance, it asserts that the total energy of the universe 

 as far as man knows it is a constant quantity, subject to con- 

 tinual changes of form but neither created nor destroyed. 



That the law of the conservation of energy applies to the 

 processes taking place in the body of the animal was exceedingly 

 probable, a priori, and has been demonstrated experimentally 

 by the researches of Rubner upon dogs, of Laulanie on various 

 animals, of Atwater, Benedict, Lusk and their associates upon 

 men and of Armsby and Fries upon cattle. 1 The impor- 

 tance of this fact in relation to the study of energy changes in 

 the body is obvious. 



1 Compare the writer's Principles of Animal Nutrition, pp. 263-268 and Penna. 

 Expt. Sta., Bui. 126. 



