BIOLOGY OF BACTERIA. 45 



favorable or detrimental to their existence becomes a 

 necessity. 



Conditions influencing the Growth of Bacteria. — 

 (a) Oxygen. — The majority of bacteria grow best when 

 exposed to the air. Some develop better when the air is 

 withheld; some will not grow at all where the least 

 amount of oxygen is present. Because of these pecu- 

 liarities bacteria are divisible into the 



Aerobic bacteria, those growing in oxygen. 



Anaerobic bacteria, those not growing in the presence 

 of oxygen. 



As, however, some of the aerobic forms will grow al- 

 most as well without oxygen as with it, the term optional 

 (facultative) anaei r obics has been applied to the special 

 class made to include them. 



As examples of strictly aerobic bacteria the Bacillus 

 subtilis and the Bacillus aerophilus may be given. These 

 forms will not grow if oxygen is denied them. The 

 staphylococci of suppuration and the bacilli of typhoid 

 fever, pneumonia, and anthrax, as well as the spirillum 

 of cholera, will grow almost equally well with or with- 

 out oxygen, and hence belong to the optional anaerobics. 

 The bacillus of tetanus and of malignant edema, and the 

 non-pathogenic forms, the Bacillus butyricus, Bacillus 

 muscoides, and Bacillus polypiformis, will not develop 

 at all where any oxygen is present, and hence are 

 strictly anaerobic. 



(b) Nutriment. — The bacteria do not seem able to derive 

 their nourishment from purely inorganic matter. Pros- 

 kauer and Beck, however, have succeeded in growing the 

 tubercle bacillus in a mixture containing ammonium 

 carbonate 0.35 per cent., potassium phosphate 0.15 per 

 cent., magnesium sulphate 0.25 per cent., glycerin 1.5 

 per cent. They grow best where diffusible albumins are 

 present. The ammonium salts are rather less fitted to 

 support them than their organic compounds. The in- 

 dividual bacterium varies very widely in the nutriment 

 which it requires. Some of the water-microbes can live 



