68 BACTERIAL METABOLISM 
Those bacteria habitually pathogenic for man induce less striking 
physical and chemical changes in their environment, as a rule, than 
do the saprophytic types, as Theobald Smith^ showed long ago. Thus, 
typhoid bacilli are relatively inert culturally; they form no gas in 
sugar media, no indol, and do not liquefy gelatin; on the contrary, B. 
coli and even more strikingly B. pro tens are characterized by striking 
cultural changes; B. coli produces deep-seated changes in protein, 
resulting in the production of indol; it produces gas from sugar media, 
but it does not liquefy gelatin. B. proteus behaves much like B. coli 
in sugar media, but liquefies gelatin as well. These marked changes 
in the composition of the medium, namely, the production of indol 
from protein, the production of gas from sugar, and the liquefaction 
of gelatin, are all phenomena associated with the vegetative or energy 
phase of bacteria. 
n. THE NATURE OF BACTERIAL METABOLISM. 
Chemically considered, the anabolic phase of bacterial activity is 
one characterized by the synthesis of relatively simple substances, 
chiefly nitrogen-containing, into the complex specific bacterial pro- 
toplasm through a series of synthetic reactions among which reduc- 
tions and condensations appear to be the more prominent. It is 
very probable that many of these condensation reactions are hydro- 
genic in nature; that is, two simpler molecules are united into one 
molecule of greater complexity through the removal of hydrogen and 
oxygen from them in the proportions to form water. 
As simple illustrations: the formation of lactose from a molecule 
each of glucose and galactose, 
CeHnOe + CeHnOe = C12H22O11 + H2O 
Glucose. Galactose. Lactose. 
the formation of a polypeptid, glycyl-glycin, from two molecules of 
glycocoll,^ 
NH2.CH2.COOH + H.NH.CH2.COOH = NH2.CH2CO.NH.CH2.COOH + H2O 
and the formation of the glyceride of a fatty acid from glycerol and 
acetic acid may be cited, 
CH2.OH + HOOC.CH3 = CH2.0.OC.CH3 
I I 
CH.OH + HOOC.CH3 = CH.O.OC.CH3 + 3H2O 
I I 
CH2.OH + HOOC.CH3 CH2.O.OC.CH3 
Glycerin. Acetic acid. Triacetin. 
Recently, Xeuberg^ has shown that yeasts are capable of bringing 
about syntheses of organic compounds in the presence of carbohydrates: 
for example, benzaldehyde and acetaldehyde condense to form a new 
1 Fermentation Tube, Wilder Quarter Century Book, 1893, p. 219. (See also Kendall, 
Day and Walker: Jour. Am. Chem. Assn., 1913, 35, 1201-1249, for analytical data.) 
2 Fischer: Ber. d. deutsch. chem. Gesell., 1906, 39, 530. 
' See Neuberg and Kobel: Handb. d. biol. Arbeitsmeth., abt. iv, 1927, p. 625. 
