38 GENERAL PHYSIOLOGY OF BACTERIA 



perpetuation of the organism during periods of environmental unfit- 

 ness. Whether spore formation is a definite phase in the life-history of 

 spore-forming bacteria is not definitely settled. Sporulation is rarely 

 observed when the temperature of the environment falls much below 

 15 C., although considerable latitude is observed among the spore- 

 forming bacteria in this respect. Spores are rarely, if ever, produced 

 within the tissues of the animal body : if the tissues are exposed to 

 the air, however, particularly postmortem, spore formation may take 

 place. No bacteria progressively pathogenic for man are known to 

 form spores. 



The unusual resistance of mature spores to desiccation, to exposure 

 to dry and moist heat, and to disinfectants may be due either to 

 their low content of water, for spores contain less than half of the 

 water contained in the normal vegetative cell, to the relatively thick 



og 



FIG. 4. Germination of bacterial spores. 1, by absorption of spore membrane; 

 2, equatorial germination; 3, polar germination. 



refractile spore membrane, or to unusual concentrations of fatty and 

 lipoidal substances. Experiments by Lewith 1 would suggest that the 

 relative desiccation of the contents of spores as compared with the mois- 

 ture content of the vegetative organism would be the most plausible 

 explanation of their resistance to heat without apparent injury. He 

 found that egg albumen (dried) suspended in 5 per cent, of water coagu- 

 lated at 145 C.; suspended in 18 per cent, of water, coagulation took 

 place at 90 C.; with 25 per cent, of water, at 80 C.; and in a consider- 

 able volume of water (amount not stated) coagulation occurred when 

 the temperature reached 56 C. 



The resistance of spores to physical conditions varies somewhat 

 according to the organism in which they are formed. Generally 

 speaking, however, several minutes' exposure to the temperature 

 of boiling water (100 C.) may fail to kill them. Dry heat is less 

 effective than moist heat, for an exposure of 160 C. for one and one- 

 half hours is required to certainly sterilize glassware containing spores. 

 Ten to fifteen pounds live steam pressure for fifteen minutes is required 



1 Arch. f. exp. Path. u. Pharmakol., 1890, xxvi. 



