PROPERTIES OF PROTOPLASM 11 



heat is liberated. The potential energy thus changed into light 

 and heat was stored up in the coal, ages ago when it was a part 

 of the earth's vegetation. This process of physical combustion 

 is brought about by the union of oxygen (oxidation) with vari- 

 ous elements in the coal. Smoke, carbon dioxide (C0 2 ), water 

 (H 2 O), and an incombustible residue (ash) are formed, while 

 kinetic energy is given off in the form of light and heat. Here 

 then, with oxidation is a change from potential, or stored, to 

 kinetic or free energy, while an organic material with definite 

 properties is changed at the same time into CO 2 , H 2 O, free 

 carbon and a useless residue. 



The famous French chemists, Lavoisier and Laplace, in 1780, 

 were the first to show that animal heat, like that from fire, is 

 produced by combustion involving the consumption of oxygen 

 and the liberation of CO 2 , and they found that practically the 

 same amount of heat was produced and the same amount of 

 C0 2 was liberated by a living Guinea pig and by a burning 

 candle. Later, it was discovered that another product occurs 

 in the living animal, viz. urea. 



The actively moving, eating, digesting and excreting Para- 

 mecium gets the energy for its many vital processes through 

 the oxidation of substances contained in its protoplasmic make- 

 up. As in the combustion of coal, CO 2 and H 2 O are formed and 

 liberated while an incombustible residue, termed urea, is analo- 

 gous to ashes in physical combustion. The energy for move- 

 ments and for carrying on the many physiological activities of 

 the organism is derived from the chemical energy contained in 

 the complex molecules forming the basis of all protoplasm. The 

 continued activity of Paramecium without a new supply of fuel 

 (food) results in the burning out of the protoplasmic substance 

 as shown by the vacuolization of the body, final exhaustion of 

 the available elements for combustion, and must result in death 

 (Figs. 2 and 3). Similar processes take place in all animals and 

 plants; C0 2 , H 2 0, and urea or equivalent are formed and ex- 

 creted in one way or another, while many of the complexities 

 in structure of the higher animals are due to the elaboration of 

 organs for the disposal of such waste products. 



