CHEMICAL COMPOSITION OF BACTERIA 57 
It will be seen that from 75 to 86 per cent of the bacterial cell is 
water. The remainder of the cell consists chiefly of protein, carbo- 
hydrate-like bodies,' extractives (fats, fatty acids, waxes and lipoids) 
and inorganic salts. Of these, the nitrogenous sulistances vary greatly 
in amount, depending upon the composition of the medium in which 
the organisms are grown. The extractives (fats, waxes, lipoids and 
fatty acids) are most prominent in the tubercle bacillus and the acid- 
fast group. Some extractives, however, are found in all bacteria, 
they being generally greater in amount on a medium containing car- 
bohydrate and protein than on one containing protein alone. The 
chemical determination of the extracti\'es is very unsatisfactory, 
partly because of the difficulty in breaking up the cell sufficiently to 
facilitate the entrance of the solvent. 
3. Chemical Composition of Bacteria.— The percentages of the ele- 
ments and various constituents of bacteria, as indicated in the above 
tables, is at best only approximate. Other factors very markedly 
influence the composition of the organisms. Dawson- found that the 
composition of bacteria varied both with respect to the medium in 
which cultivation was practised, and, also, different bacteria varied 
among themselves in their composition. 
The age of the culture, the temperature at which it is grown, and the 
composition of the medium in which the organisms are grown are also 
very important. Generally speaking, young cultures appear to con- 
tain rather more dry residue than older cultures, and bacteria grown 
at 37° C. contain more dry residue than those grown at 20° C.^ The 
inorganic constituents of the broth influence the composition of bacteria 
markedly. Cramer^ has found that the percentage composition of the 
ash of the cholera vibrio varies within very considerable limits as the 
organism is grown under different conditions. The following table 
indicates in a general way the influence of these factors: 
Ash content of bacteria in dry substance 
Ash content of moist mass .... 
Ash content of medium in moist mass 
Phosphoric acid in bacterial ash . 
Phosphoric acid in media ash 
Chlorine in bacterial ash 
Chlorine in media ash 
w 
2 
. 
OJ .O 
• -O 
IM 
O-g =3 . 
flJ3 c3 
S M a; ft 
2 t" o 
J2 c3 o 
lUl 
fill 
Wk 
^ tf^ 
£«^ 
^«co 
9.30 
22.30 
25.90 
1.34 
2.75 
3.73 
1.25 
2.50 
4.12 
28.70 
34.80 
10.90 
7.90 
7.97 
2.10 
16.90 
39.80 
40.70 
23 . 00 
11.40 
49.20 
1 For the synthesis of starch by bacteria see Grey: Biochem. Jour., 1924, 18, 712. 
2 Jour. Bacteriol., 1919, 4, 133. 
' The decrease in dry residue observed in old cultures is partly attributable to auto- 
lysis of bacteria; this is usually observed earlier in cultures maintained at 37° C. than in 
corresponding cultures kept at 20° C. Growth is more rapid at this higher temperature, 
and recessive changes due partly to the accumulation of waste products are seen earlier. 
^ Arch. f. Hyg., 1895, 22, 167. 
