FUNGI 133 



dividuals in a comparatively short time that it is impossible 

 to imagine what would happen if bacteria were left free 

 to reproduce to their full capacity. Bacteria have been 

 observed to reproduce themselves in fifteen to forty minutes 

 after their formation; that is, a single generation of such 

 bacteria is that length of time. It would be interesting 

 to determine the number of progeny from a single bacterium 

 at the end of twenty-four hours, if such a rate were main- 

 tained. When nutrition fails, many bacteria have the 

 power of passing into a protected condition, a portion of the 

 protoplasm within the cell separating from the rest and 

 becoming surrounded by a thick membrane (Fig. 122). 

 The rest of the cell finally disorganizes and this internally 

 formed cell persists. It has received the name of "spore," 

 but is not to be regarded as a spore in the usual sense. A 

 single bacterium produces only one such spore, and when 

 this spore again encounters favorable conditions it produces 

 in turn only a single bacterium. This "spore," therefore, 

 is only an inactive and protected condition of the bacterium. 

 It is of great importance to determine the power of 

 resistance of bacteria and of their more resistant "spores," 

 and there is great variation in this regard. Drying and 

 cold kill many, but not all. For example, it is known that 

 the bacterium of typhoid fever (Fig. 121, F) can endure 

 freezing in a block of ice for months and become active again 

 when the ice melts; and for this reason the source of ice 

 used in drinking water should be considered as carefully as 

 the source of the water itself. Moist heat, however, as 

 boiling or steaming, has been found to be most efficient in 

 killing bacteria; and so the boiling of water and the cooking 

 of food are usually ample safeguards against them. The 

 so-called disinfectants are chemicals that destroy bacteria. 

 It is the knowledge of such facts that has developed what is 

 called antiseptic surgery, which is the use of various means 

 to exclude bacteria and so prevent inflammation and decay. 



