22 LIFE AND LIGHT 



act we perform, and there is no form of energy so universally dis- 

 tributed upon the earth and so indispensable as biotic energy. 



In studying this interesting form of energy and its manufactured 

 products, the first fundamental question cropping up is the manner 

 in which it is produced, and the energy form or forms transformed 

 into it in order to keep up the supply as the stores are utilised and 

 reconverted into the simple inorganic forms. 



Let us get down to fundamental facts, and from these trace 

 upwards over the many unknown lacunae, as far as our present know- 

 ledge will allow us, to the energy transformer endowed with that 

 property which we call life. 



In any ordinary transformation of energy from one type to 

 another three things are essential, and this is also true of those 

 changes in which biotic energy is involved. These three things are a 

 suitable energy transformer, such as a water-wheel, turbine, steam- 

 engine, dynamo, or living cell; secondly, a type of matter which is 

 to be the habitus of the energy in each case, or a reservoir for it, 

 such as the water, or steam, or electric wire, or colloid aggregates of 

 the cell ; and, thirdly, a source of energy in another type, such as 

 chemical energy (in the form of coal, spirit, petrol, food, etc.), or 

 sunlight, or other type of radiant energy. 



Now, whatever secondarily may be the form of energy supplied 

 to the cell, primarily all biotic energy is dependent upon sunlight. 

 Coal, petroleum, spirit, organic foodstuffs, the nitrates of the soil 

 even, all are derived from the sun's energy. 



Next, in regard to the material used for the habitation of this 

 energy, the most essential constituents are most simple in their 

 chemical nature, and consist of carbon dioxide from the atmo- 

 sphere and water taken usually from the earth, holding in solution a 

 few simple salts, such as nitrates, phosphates, sulphates, chlorides, 

 and silicates of ammonium, sodium, potassium, iron, calcium, 

 manganese, magnesium, aluminium, and a few other elements in 

 minute traces. Most abundantly taken up and manipulated in the 

 process are the four elements carbon, hydrogen, oxygen, and 

 nitrogen ; small amounts only of the others are required, but they 

 are none the less essential and indispensable. 



It is a most remarkable and interesting fact that the whole life 

 of the world, as at present constituted, is dependent upon the 

 presence of a mere trace of carbon dioxide in the atmosphere. This 

 carbon dioxide, which is the gas produced when carbon or charcoal 



