THE CHARACTERISTICS OF BACTERIA 47 



C. Physiology. 



1. Relation to oxygen. 



2. Relation to light, desiccation, etc. 



3. Pigment production. 



4. Gas production. 



a. In shake culture. 



b. In fermentation tube : growth in open arm ; growth 

 in closed arm. 



c. Ratio of H : CO . 



FIG. 26. Types of internal structure of colonies 



A, areolate ; B, grumose ; C, moruloid ; D, clouded ; E, gyrose ; F, marmorated ; 



G, reticulate 



5. Acid or alkali production. 



a. Litmus milk. 



6. Reduction of nitrates to nitrites, to ammonia, or to free 

 nitrogen. 



7. Indol production. 



8. Habitat. 



