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 caretully 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. 
