AEROBIC RESPIRATION 241 
tute fermentation and the energy therefrom is available for cell use. 
Fermentation may then be regarded as respiration if the latter term is 
considered to cover those processes which yield energy. There are two 
kinds of respiration, aerobic respiration and anaerobic respiration. 
Aerobic Respiration. This involves the securing of energy from 
food substances by means of and in the presence of free oxygen. In 
order to present the facts required in a discussion of this nature, the 
carbohydrates lend themselves very well. It must be remembered, 
however, that there are certain well-known objections to the expression 
of bacterial changes by chemical equations and these should be borne 
in mind in considering the equations which follow. Asa typical example 
of aerobic respiration the decomposition of dextrose may be taken 
CoeHi1206+ 602 =6CO2+6H20+674 cal. In this change molecular oxy- 
gen has been used to burn dextrose completely.* 
In the products carbon dioxide and water there is no energy which is 
available for bacteria. With nitrogenous substances the oxidation of 
glycocoll takes place as follows: 
H 
| p> 
H—C—C=-OH + 30 = 2CO2 + H20 + NH3 + 152 Cal. 
NHoe 
In this equation allowance must be made for the combustion heat of 
ammonia since this compound may be further oxidized. Leucin is 
oxidized as follows: 
CeHisNOe+150 = 602+5H20+NH3+755 cal. 
In this equation the same correction must also be made for the com- 
bustion heat of ammonia. 
Hydrogen sulphide is oxidized by the sulphur bacteria according to 
the following equation: 
H28+202 = H2804+ 207 cal. 
or to neutral sulphur as follows: 
H2S+0 = H20+65 cal. 
* In all considerations of respiration, it must be remembered that the energy 
secured by complex molecules is latent in them, having been put into them by the 
organism which formed them. Such synthetic processes are endothermic for the 
organism which builds up these complex substances from the simpler compounds. 
The bacteria secure this energy when they split these complex compounds to simpler 
ones. 
