242 
human body, are caused by minute organisms which live, many 
of them move, grow, and nee within the tissues of our 
bodies. These organisms are kno a general way as bacteria. 
The bacteria are the smallest ae living organisms and can 
be studied only with the aid of a powerful microscope, and for this 
Fic, 33. The mycelium or growing phase of a fungus. 
reason the science of bacteriology is of comparatively recent origin. 
The reproduction of the bacteria is a very simple process: an indi- 
vidual attains mature size and divides or breaks into two; each of 
the offspring again attains mature size and the process is repeated. 
One of the chief characteristics of the bacteria is their physiology, 
