MOISTURE AND DESICCATION 39 
D. LONGEVITY. 
The duration of life in the indivickial non-spore-forming bacterium 
is unknown, but it is greatest apparently when the organism is quies- 
cent or nearly so. The viability of bacteria upon artificial media is 
dependent in part upon the temperature; the more common patho- 
genic microbes remain alive for one to several months when they are 
kept at temperatures slightly above freezing in a dark place. 
Spores have been dried and kept in a cool dry place for more than 
two decades, and yet developed with their usual luxuriance when 
placed in a favorable environment. Dried anthrax spores thus retain 
not only their viability but their virulence unimpaired for years. 
Swann^ states that 55 per cent of anthrax spores kept in a cool, dry 
place, die within twelve months. Practically, the average duration of 
life among bacteria is comparatively brief .^ 
E. MOISTURE AND DESICCATION. 
Bacteria normally contain at least SO per cent of moisture in their 
substance, and they develop typically only in media containing con- 
siderable amounts of moisture. Bacteria do not vegetate normally in 
desiccated media, but many varieties resist drying for considerable 
periods. Advantage is taken of the restriction of bacterial develop- 
ment in the absence of suitable amounts of moisture in various pro- 
cesses of drying meats and other foodstuffs; desiccated foods will keep 
for weeks under the proper conditions. Bacterial spores protected 
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. 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. 
1 Jour. Pathol, and Bacteriol., 1924, 27, 130. 
- See Omeliansky: Arch, des 8ci. biol., St. Petersburg, 1011, 16, 355 for an interesting 
bacteriological study of a mastodon. 
' Fischer: Vorlesungen iiber Bakterien, 1903, II Aufl., 110. 
