F. Osmotic pressure conditions, though modifying decidedly the growth of bacteria, are not usually studied as aids in their recognition, nor are the effects of various forms of energy, such as light, electricity, x-rays, etc.
Among the “Physiological Activities” discussed in [Chapters IX–XII] those which, in addition to the staining reactions described, are of most use in the identification of non-pathogenic bacteria are the first ten listed below. For pathogenic bacteria the entire thirteen are needed.
1. Liquefaction of gelatin.
2. Digestion of blood serum.
3. Coagulation and digestion of milk.
4. Acid or gaseous fermentation in milk, or both.
5. Acid or gaseous fermentation of various carbohydrates in carbohydrate broth, or both.
6. Production of indol in “indol solution.”
7. Production of pigments on various media.
8. Reduction of nitrates to nitrites, ammonia, or free nitrogen.