54 Biology of Micro-organisms 



Aerobes, which grow in the presence of uncombined oxygen, and 



Anaerobes, which do not grow in the presence of uncombined 

 oxygen. 



As, however, some of the aerobic forms grow almost as well with- 

 out free oxygen as with it, they are known as optional (facultative) 

 anaerobes. 



As examples of strictly aerobic bacteria Bacillus subtilis. Bacillus 

 aerophilus, Bacillus tuberculosis, and Bacillus diphtherias may be 

 given. These will not grow if oxygen is denied them. The cocci of 

 suppuration, the bacillus of t3fphoid fever, and the spirillum of 

 cholera grow almost equally well with or without free oxygen, and 

 hence belong to the optional anaerobes. The bacilli of tetanus and of 

 malignant edema and the non-pathogenic Bacillus butyricus, 

 Bacillus muscoides, and Bacillus polypiformis, will not develop at 

 all where any free oxygen is present, and hence are strictly anaerobic. 



The higher bacteria, oidia, molds and protozoa, are for the most 

 part aerobes and optional anaerobes. Treponema pallidum seems to 

 be a strictly anaerobic protozoan. 



Food. — The bacteria grow best where diffusible albumins are 

 present, the ammonium salts being less fitted to support them than 

 their organic compounds. Proskauer and Beck* have succeeded 

 in growing the tubercle bacillus in a mixture containing ammonium 

 carbonate 0.35 per cent., potassium phosphate 0.15 per cent., mag- 

 nesium sulphate 0.25 per cent., and glycerin 1.5 per cent. Some of 

 the water microbes can live in distilled water to which the smallest 

 amount of organic matter has been added; others require so con- 

 centrated a medium that only blood-serum can be used for their 

 cultivation. The statement that certain forms of bacteria can 

 flourish in clean distilled water seems to be untrue, as in this 

 medium the organisms soon die and disintegrate. If, however, in 

 making the transfer, a drop of culture material is carried into the 

 water with the bacteria, the distilled water ceases to be such, and 

 becomes a diluted bouillon fitted to support bacterial life for a time. 

 Sometimes a species with a preference for a particular culture 

 medium can gradually be accustomed to another, though immediate 

 transplantation causes the death of the organism. Sometimes the 

 addition of such substances as glucose and glycerin has a peculiarly 

 favorable influence, the latter, for example, enabling the tubercle 

 bacillus to grow upon agar-agar. 



The yeasts grow best upon media containing sugars, but can also 

 be cultivated upon media containing diffusible protein and non- 

 fermentable carbohydrates and glycerin. 



The molds flourish upon almost all kinds of organic matter, but 

 perhaps attain their most rapid development upon media containing 

 fermentable carbohydrates. 



The saprophytic and parasitic protozoa live by osmosis and absorb 

 * "Zeitschrift flir Hygiene," etc., Aug. 10, 1894, vol. xviii. No. i. 



