228 PRINCIPLES OF ANIMAL NUTRITION. 
of heat. That branch of science which deals with the connection 
between chemical and thermal processes is known as thermo-chem- 
istry. Since kinetic energy in the animal is derived from chemical 
processes, and since it largely takes the form of heat, we may regard 
the study of the transformations of energy in the organism as con- 
_ stituting a branch of thermo-chemistry and proceed to a consider- 
ation of the fundamental laws upon which the latter subject is 
based. 
THE CONSERVATION OF EneRGy.—In any system of bodies not 
acted on by external forces the sum of the potential and kinetic 
energy is constant. In other words, while the ratio of potential 
to kinetic energy may vary, and while each may take various forms, 
as mass-motion, heat, electric stress, etc., there is no loss of energy 
in these conversions. Energy, like matter, is indestructible. This 
great law of the conservation of energy was first clearly enunciated 
by Mayer, and forms the foundation of all modern conceptions of. 
physical processes. In the case of the swinging pendulum used 
above as an illustration the total-energy of the system composed 
of the earth and the pendulum is constant, a portion of it simply 
alternating between the potential and kinetic states. So, too, in 
the system of atoms of carbon, hydrogen, and oxygen, the potential 
energy contained in the system before the starch is burned is simply 
converted into the kinetic energy of heat, while the total energy 
of the system remains the same. 
INITIAL AND Finau States.—An important consequence of the 
law of the conservation of energy, which was first deduced and 
demonstrated experimentally by Hess in 1840, is known as the law 
of initial and final states. This law is that in any independent 
system the amount of energy transformed from the potential to 
the kinetic form, or vice versa, during any change in the system, 
depends solely upon the initial and final states of the system and 
not at all upon the rapidity of the transformation or upon the kind 
or number of the intermediate stages through which it passes. 
Although this law is true in the general form here stated, it was 
originally propounded as related to chemical reactions and forms 
the basis of the science of thermo-chemistry. If we start with 
starch and oxygen and end with the corresponding quantities of 
carbon dioxide and water, the amount of kinetic energy evolved is 
