40 GENERAL PHYSIOLOGY OF BACTERIA 



tected from direct sunlight are extremely resistant to drying, but 

 they develop with characteristic vigor when environmental conditions 

 become suitable. Even non-sporogenic bacteria may develop after 

 days or weeks of desiccation. Many pathogenic bacteria are eliminated 

 from the body enveloped in albuminous material, as in sputum. These 

 organisms thus protected may resist drying for many days, provided 

 they are not exposed to direct light. The following table indicates 

 the relative viability of various bacteria pathogenic for man to air 

 drying. 1 



1. Gonococcus, few hours. 



2. Cholera vibrio, few hours to two days. 



3. Plague bacillus, one to eight days. 



4. Diphtheria bacillus, twenty to thirty days. 



5. Streptococcus pyogenes, fourteen to thirty-six days. 



6. Pneumococcus, nineteen to fifty-five days. 



7. Staphylococcus pyogenes, fifty-five to one hundred days. 



8. Typhoid bacillus, up to. seventy days. 



9. Tubercle bacillus, two to three months. 



F. OXYGEN: AEROBIOSIS AND ANAEROBIOSIS. 



Oxygen, either in the free state or combined, is essential to the 

 growth of all known bacteria. The majority of bacteria grow best in 

 the presence of free (atmospheric) oxygen, although the percentage 

 of this gas necessary to support bacterial life may be considerably 

 less than that occurring normally in the air. Some bacteria appear 

 to be wholly dependent upon free oxygen, and they are called obligate 

 aerobes. A small group of bacteria, on the contrary, grow only in the 

 absence of free oxygen, and more than minimal concentrations of this 

 gas are actually poisonous to them. Those bacteria which grow only 

 in the absence of free oxygen are called obligate anaerobes. The vast 

 majority of bacteria are facultative with respect to their oxygen 

 requirement, growing best in the presence of atmospheric oxygen but 

 able to develop either in the presence of small amounts of free oxygen, 

 as in the tissue of the body and certain parts of the intestinal tract, 

 or they are able to obtain their oxygen from chemical compounds, as 

 certain simple sugars, if free oxygen is not available. These organisms 

 are called facultative anaerobes. The maximum tolerance of bacteria 

 for oxygen varies very considerably, as the following table indicates : 



Oxygen content of the air is taken as 100 per cent. 



1 Fischer, Vorlesungen iiber Bakterien 1903, II Aufl., 110. 



