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 various 

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

 (H2O), 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 C02, H^O, free 

 carbon and a useless residue. 



The famous French chemists, Lavoisier and Laplace were the 

 first in 1780 to show that animal heat, like that from fire, is 

 produced by combustion involving the consumption of oxygen 

 and the liberation of CO2, and they found that practically the 

 same amount of heat was produced and the same amount of 

 C02 was liberated by a living guinea pig and 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, C02 and H^O are formed and 

 liberated while an incombustible residue termed urea ; is analogous 

 to ashes in physical combustion. The energy for movements and 

 for carrying on the many physiological activities of the organism 

 is derived from the potential 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; CO2, EkO, 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. 



