MOISTURE AND DESICCATION 39 



to effect sterilization of liquids and organic matter in general. Direct 

 sunlight will kill spores after days of exposure. 



Germination of bacterial spores takes place when they are placed 

 in a suitable nutritive environment in which the temperature, moisture 

 and oxygen relations are favorable. The vegetative cell breaks through 

 the spore membrane apparently after the latter has lost its refractility, 

 and reproduction by fission proceeds anew, and persists until environ- 

 mental conditions again lead to sporulation. 



D. LONGEVITY. 



The duration of life in the individual non-spore-forming bacterium 

 is unknown, but it is greatest apparently when the organism is quiescent 

 or nearly so. This condition is realized most commonly when bacteria 

 are exposed to temperatures slightly above freezing in a dark place. 

 This question has been studied recently under unusual conditions. 

 A mastodon was discovered in Siberia which had been uncovered by 

 an unusual recession of the ice. This animal was found to be practi- 

 cally intact, and cultures made with proper precautions from the 

 center of the proboscis contained bacteria indistinguishable from 

 Sarcina lutea and other well known air organisms. 1 If these cultures 

 are authentic, a most unexpected instance of bacterial longevity has 

 been unearthed, for this animal has undoubtedly been frozen for 

 hundreds of years. 



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. Practically, 

 the. average duration of life among bacteria is comparatively brief. 



E. MOISTURE AND DESICCATION. 



Bacteria normally contain at least 80 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 pro- 



1 Russian Academy of Science, 1911-1912. 



