CELL MULTIPLICATION 123 
of sugar is broken into carbon dioxide and water, as shown in the 
equation C.6H,.0, + 6 O. = 6 CO. + 6 H,O. In respiration the 
breaking of the sugar into carbon dioxide and alcohol is probably 
the first step which is then followed by the breaking of the alcohol 
into carbon dioxide and water. From the equation in case of the 
fermentation of sugar it is seen that the energy is obtained by 
uniting the oxygen and carbon, both of which are present in the 
molecule of sugar. Thus by the use of the oxygen within the 
compound broken down, some oxidation can occur when there is 
no oxygen available from without. 
Instead of alcohol other substances may be produced by fer- 
mentation according to the nature of the fermenting organism 
and the kind of compound fermented. Thus in the fermentation 
of cider by certain kinds of Bacteria alcohol is first produced and 
later acetic acid. In the souring of milk the Bacteria break the 
milk sugar into lactic acid. Although sugars are the substances 
involved most in fermentation, other compounds are known to be 
involved. Even decay, caused principally by Molds and Bac- 
teria, is regarded as a kind of fermentation, in which case many 
kinds of substances are involved. 
The injury caused by Fungi and Bacteria is often due largely to 
the by-products of their respiration and growth. Partly in this 
way Fungi damage or destroy plants upon which they live. Many 
of the Bacteria associated with diseases produce poisons known 
as toxins which cause injury or death in animals and sometimes 
in plants. To combat some of these toxins antitoxins are used. 
Thus respiration whether aérobic or anaérobic is that oxidation 
process by which cells secure energy to carry on their work. Any 
condition, such as a low or high temperature, absence of food, or 
lack of oxygen, which hinders respiration, holds cell activity in 
check and thus impedes plant growth. Furthermore, due to the 
liberation of heat and moisture which may become destructive 
when allowed to accumulate, respiration must be reckoned with 
in the storing of plant products. 
Cell Multiplication 
As previously stated (page 112), cells are exceedingly small 
structures and a small size seems preferable in both plants and 
animals where numerous small cells rather than a few large ones 
