CHAPTER IV. 
BACTERIAL METABOLISM. 
I. 
General. 
VI 
II. 
The Nature of Bacterial Metab- 
olism. 
III. 
Nitrogen Metabolism. 
IV. 
Carbon Metabolism. 
VII 
V. 
Qualitative Catabolic Reactions 
of Bacteria. 
VIII 
A. In Media Containing Only 
Utilizable Nitrogenous Sub- 
IX 
stances. 
B. In Media Containing Both 
Utilizable Nitrogenous Sub- 
stances and Utilizable Car- 
bohydrates. 
The Qualitative Influence of 
Utilizable Carbohydrates Up- 
on THE Elaboration of Proteo- 
lytic Enzymes. 
Quantitative Measure of Bac- 
terial Metabolism. 
The Significance of Bacterial 
Metabolism. 
Fermentation and Putrefaction. 
I. GENERAL BACTERIAL METABOLISM. 
Two distinct phases may be recognized in the life-history of a 
bacterial cell; an anabolic or constructive phase, during which the 
cell becomes morphologically complete; and a catabolic, vegetative, 
or fuel phase, in which the mature organism reacts chemically upon 
its environment to provide the energy (fuel) necessary for the main- 
tenance of the cell. Chronologically, the anabolic phase precedes the 
catabolic phase; that is to say, the bacterial cell must be morpho- 
logically complete before it can bring about its characteristic energy 
transformation; practically the two phases overlap somewhat. 
The actual amount of material required for the anabolic phase of 
the bacterial cell is very small, for the actual weight of the average 
bacterium is but 0.0000000016 of a milligram (see page 26). The 
structural phase is practically ended, aside from the replacement of 
comparatively slight losses of substance incidental to the elaboration 
of soluble enzymes or to additional requirements for the formation of 
structural elements, such as capsules, when the organism is morpho- 
logically complete. The waste incidental to the utilization of material 
for purely anabolic needs is likewise very small in amount, and the total 
environmental change attributable to the purely constructive phase of 
bacterial metabolism is slight, and ordinarily disregarded.^ 
The amount of material required for the catabolic (vegetative or 
energy) phase of the bacterial cell, on the contrary, is relatively large. 
The energ-y requirement of cellular organisms varies rather with the 
area of their surface than according to their actual volume; conse- 
quently, very minute organisms, as bacteria, in which the surface is 
1 Kendall: Physiol. Reviews, 192.3, 3, 438. 
