412 Transactions of the Boyal Society of South Africa. 
metabolism of the cell, as the result of the sum of all the metabolic 
processes is always an evolution of heat, which is, of course, easily apparent 
in the bodies of higher animals. Also in some plants under certain con- 
ditions the evolution of heat can be demonstrated. The excess of heat in 
plants is probably used up to further transpiration, especially in the green 
parts of plants. Transpiration, which is a form of evaporation, requires 
heat, and probably in the ordinary way water would not evaporate quickly 
enough for the plant's needs. It is hardly likely that any radiation of 
heat takes place from leaves, as leaves are usually at a slightly lower 
temperature than the surrounding atmosphere, so that instead of leaves 
giving out heat they would be more likely to absorb it. Some of the 
excess energy may be used to produce the osmotic forces manifest in cells, 
or again some may be used to prepare the dissociated atoms of katabolism 
for chemical union. 
In animals the food consists of already combined organic compounds, 
and the metabolism of animal cells may therefore be compared with that 
taking place in colourless vegetable cells — the metabolism in both cases 
being based upon chemical changes involving a liberation and redistribu- 
tion of energy. 
Whether the energy present in atoms and molecules comes originally 
from the sun is not the point under consideration in this paper. I have 
endeavoured to establish the new theory that the energy of the sun's 
rays is not used either directly or indirectly in the metabolism, say of 
a germinating seed. It is the energy present in atoms and molecules 
which is released by some chemical union that is available in cell 
metabolism. Energy is no more stored away in coal or starch than it 
is in the oxygen which is required to combine with it during com- 
bustion. Every block of stone, for that matter, may be said to contain 
energy if one could only find some element to combine with it as easily 
as oxygen combines with coal. It is perhaps best to consider that each 
oxygen atom (or any other atom) contains a certain definite amount of 
energy at a certain temperature. Energy in the form of heat is either 
added to or taken from every oxygen atom according as the surrounding 
temperature rises or falls. When a carbon atom unites with another atom 
or group of atoms it loses some of its energy, whilst during dissociation of 
a carbon compound the carbon atom before it becomes free must have 
sufficient energy restored to it to bring it back to its normal amount for 
that particular temperature. The amount of energy in an atom is constant 
for all atoms of the same kind, but it is more than probable that the 
amounts are different for different atoms. Energy in the form of emana- 
tions is continually given off from radio-active elements. This is the only 
case known so far in which energy is available without chemical union, 
but even here the energy is probably a manifestation of chemical change — 
the element radium, for instance, changing into another element. 
