12 ORGANISMS AND ENERGY. 
animals, mean an enormous and ceaseless expenditure of 
energy, and the question naturally arises, Whence is this 
energy obtained ? 
We find that the chemical decomposition of the 
constituents of protoplasm, such as proteids, results in a 
setting free of chemical energy. We have seen that pro- 
teids and less complex carbohydrates are brought directly 
into the body of the animal as food, so we are forced to 
look beyond the animal itself for the source of energy. 
On the other hand, these complex carbon compounds 
are built up or manufactured by the plant from simple 
constituents within it. In this building-up the same 
amount of energy has to be supplied as is again set free 
in movement and heat in the subsequent decomposition. 
This building-up, or the chief part of it, is effected in the 
plant by a process not fully understood, but certainly 
requiring a supply of radiant energy from the sun’s rays. 
Hence we are led to two important conclusions :— 
1. The animal kingdom is entirely dependent (or parasitic) upon 
the vegetable kingdom for all its energy. 
2. The vegetable kingdom accumulates vast stores of energy in the 
formation of complex chemical compounds, derived from the 
radiant energy of the sun. 
Organisms may be regarded as complex machines for 
transmutation of energy. The work of plants is the 
transmutation of kinetic (radiant) into chemical energy, 
and that of animals is (like that of steam-engines) the 
transmutation of chemical into kinetic energy. 
We must therefore look to the sun as the sole source of 
every movement, thought or impulse of the animal creation. 
Plants and animals have the same essential living matter or 
protoplasm, but with certain marked differences in form and 
function. ‘These are more pronounced in the higher types, 
but when the simplest living organisms are studied the 
distinctions break down. Supposing the two kingdoms are 
of common descent this state of affairs is to be expected. 
We have thus passed in review the various physical, 
chemical and vital properties of living matter, as found in 
the organic world, and have noticed the main underlying 
distinctions between the vital functions of plants and 
animals. 
