78 A DISEASE GARDEN : 
1V.—Higher Bacteria— 
1. Clostridia—when the rods are fnsiforin or spindle- 
shaped. 
2. Cladothrix—when the rods are in filamentous 
forms, with pseudo branches and true spores. 
3. Lepothrix—when the rods are of great length, 
straight, but with no spores. 
4. Streptothrix—when the rods truly branch with 
occasional club-shaped thickenings. 
Classification according to (2) biology. 
I.—Saprophytes—organisms which grow on, or in de- 
caying organic matter and can exist independently of a 
living host. 
II.—Parasites—organisms which are unable to exist 
without a living host—plant or animal. 
Organisms strictly saprophytic or strictly parasitic, are 
called Obligate ; while those organisms, which, bemg sapro- 
phytic, may become parasitic, and vice versa, are known as 
Facultative. 
Classification according to (3) necessary medium—the 
necessity for pure oxygen or air. 
I.—Aerobic— organisms which grow only in the presence 
of free oxygen or air. When this is absolutely essential, 
when they are obliged to have oxygen for their existence 
they are called Obligate or Obligatory Aerobes ; but when they 
become amphibious as to the oxygen, that is live with it or 
under favourable circumstances, without it, through some 
acquired faculty they are known as Facultative Aerobes. 
II.—Anaerobic—organisms which grow without the 
presence of free oxygen or air; they can appropriate oxygen 
from the unstable organic compounds on, or in which they 
live and among them, both Obligate and Facultative varieties, 
are to be found. 
Classification according to (6) sporulation :— 
I.—Endospores are usually found in the Bacilli or rod- 
shaped organisms, and are refractile bodies in the interior 
of the rods. They are highly resistent to the action of light, 
heat and disinfectants. 
They vary in size and shape, being round, or oval or rod 
like ; they also vary in position, being sometimes central, 
