PHYSIOLOGICAL ACTIVITIES 199 



gelatin or agar puncture or stab cultures and noting whether 

 the most abundant growth is at the top, the bottom or all 

 along the line of inoculation. 



C. Reaction of the medium — acid, alkaline or neutral as 

 influencing the rate and amount of growth. 



B. The kind of medium on which the organism grows best. 



E. The effect of injurious chemicals, as various disinfec- 

 tants, on the growth. 



F. Osmotic pressure conditions, though modifying decid- 

 edly 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, a;-rays, etc. 



Among the "Physiological Activities" discussed in Chap- 

 ters IX-XII those which, in addition to the staining reac- 

 tions 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. 



9. Production of enzymes as illustrated in the above 

 activities. 



10. Appearance of growth on different culture media. 



11. Production of free toxins as determined by injection 

 of animals with broth cultiu-es filtered free from bacteria. 



12. Causation of disease as ascertained by the injection 

 of animals with the bacteria themselves, and recovery of the 

 organism from the animals. 



13. Formation of specific antibodies as determined by the 

 proper injection of animals with the organism or its products 

 and the subsequent testing of the blood serum of the inocu- 

 lated animals. 



