4O Biology of Bacteria 



As, however, some of the aerobic forms grow almost as 

 well without 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 

 diphtheriae may be given. These will not grow if oxygen 

 is denied them. The cocci of suppuration, the bacillus of 

 typhoid fever, and the spirillum of cholera grow almost 

 equally well with or without 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. 



(b) Nutriment. 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., 

 magnesium sulphate 0.25 per cent., and glycerin 1.5 

 per cent. Some of the water microbes can live in dis- 

 tilled water to which the smallest amount of organic 

 matter has been added; others require so concentrated 

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

 cultivation. The statement that certain forms of bac- 

 teria 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 bac- 

 teria, the distilled water ceases to be such, and becomes a 

 dilute 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 influ- 

 ence, the latter, for example, enabling the tubercle bacillus 

 to grow upon agar-agar. 



(c) Moisture. A certain amount of water is indis- 

 pensable to the growth of bacteria. The amount can be 



* " Zeitschrift fiir Hygiene," etc., Aug. 10, 1894, vol. xvm, No. 1. 



