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 2 . 



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 aerobic and anaerobic. Between 

 these two groups we have those that can grow either 

 with or without the access of oxygen. 



Some at least of the strict anaerobic bacteria require 



