54 BACTERIOLOGY. 
abuminoid material and less easily from ammonium 
compounds. Their carbon they derive from albumin, 
peptone, sugar and other allied carbohydrates, glycerin, 
fats, and other organic substances. It is an interest- 
‘ing fact, that even compounds which in considerable 
concentration are extremely poisonous, can, when in 
sufficient dilution, provide the necessary carbon; thus 
some derive it from carbolic acid in very dilute solu- 
tions. Another species of bacteria isolated by Wino- 
gradsky were shown by him to derive their carbon 
from CO,. 
The value of substances as a source of nutrition is 
often influenced by the presence of other materials, as, 
for instance, the value of asparagin is increased by the 
presence of sugars. Further, material from which 
nitrogen and carbon cannot be directly obtained still 
become assimilable after being subjected to the influ- 
ence of bacterial ferments. The profound and diverse 
changes produced by the different ferments make it 
almost impossible to establish, except in the most gen- 
eral way, the nutritive value of any mixture for a large 
number of bacteria through a simple knowledge of its 
chemical composition. The special culture media, such 
as bouillon, blood-serum, etc., for the development of 
bacteria will be dealt with in a later chapter. 
The relation of bacteria to oxygen: The majority abso- 
lutely require oxygen for their growth, but a consider- 
able minority fail to grow unless it is excluded. A 
knowledge of this latter fact we owe to Pasteur, who 
divided bacteria into aérobic and anaérobic. Between 
these two groups we have those that can grow either 
with or without the access of oxygen. 
Some at least of the strict anaérobic bacteria require 
