THE BALANCE OF NUTRITION 225 



is transformed into heat by its almost instantaneous burning 

 in oxygen. The answer to this question is found in what is 

 called the law of initial and final states. 



This law is that in any independent system the amount of 

 energy transformed during a 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 nor 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. If we 

 start with starch and oxygen and end with the corresponding 

 quantities of carbon dioxid and water, the amount of chemical 

 energy converted into heat or other forms is the same, no matter 

 whether the starch be burned almost instantaneously in pure 

 oxygen or whether it be subjected to slow oxidation in the tissues 

 of a plant buried in the soil ; whether carbon dioxid and water 

 are the immediate products of the action or whether the starch 

 passes through intermediate stages like maltose, glycogen, 

 dextrose, lactic acid, etc., etc., as in the body of the animal. It 

 is simply necessary to determine the difference in chemical 

 energy between the system in its initial and in its final state 

 to obtain the amount of energy transformed during the 

 change. 



313. Measurement of kinetic energy. The most common 

 method of measuring the energy liberated by a machine or an 

 animal as motion energy is its conversion, actually or virtually, 

 into gravitation energy, which is measured by the units given 

 on a previous page (308). In case of small amounts of energy 

 a weight may be actually lifted, the product of weight into 

 distance giving the number of gram centimeters or foot pounds 

 of energy expended. In other cases, the subject may pull 

 against a resistance produced, for example, by the friction of a 

 brake, the traction being measured by some form of spring 

 balance. In this case the kinetic energy is, as a matter of fact, 

 converted into heat, but the tractive pull multiplied by the 

 distance gives the equivalent number of gravitation units. In 

 still another form the subject virtually lifts his own weight by 

 climbing the inclined plane of a tread power, the body weight 

 multiplied by the distance multiplied by the sine of the angle 

 of ascent equaling the units of gravitation energy to be measured. 

 Q 



