REPRODUCTION OF BACTERIA 49 



and not always be perceptible, and this may account for the 

 formation of spores in certain cases where the environment ap- 

 pears normal. Below and above the point where sporulation 

 takes place at a temperature favorable for reproduction no 

 spores are formed, although fission may take place. 



Certain species of bacteria may be made to lose the power 

 of spore formation when grown at high temperature (Bact. 

 anthracis). Gaseous environment may also influence the 

 power of a species of bacteria to form spores. Bacterium 

 anthracis in the animal body does not form spores, but when 

 given a large amount of oxygen, on artificial media, it readily 

 forms them. 



The spore is a very resistant body. It is resistant to heat, 

 some species withstanding very high temperatures, to 

 cold, and to chemicals. Spores, as well as vegetative forms, 

 vary in their powers of resistance with the species. For example, 

 the vegetative form of Bacterium anthracis is killed by one 

 per cent phenol in two minutes, and in the spore stage it 

 requires from one to fifteen days (Koch). Anthrax spores will 

 withstand air drying for years. They are the most resistant 

 spores known. The test of efficiency of all disinfectants is par- 

 tially based on their ability to destroy anthrax spores. The 

 great resistance of the spore is due to the very compact and 

 impermeable membrane which surrounds it, and also to the fact 

 that its protoplasm contains less water than the vegetative form. 

 The more water there is in a cell the easier it is coagulated. 

 The spore is composed of condensed protoplasm. Ordinary 



