48 BACTERIOLOGY. 
the optimum of the organism to beexamined. If at the 
end of twelve, eighteen, twenty-four, thirty, thirty-six 
hours, etc., specimens of the culture are observed first 
unstained in the hanging drops, and then, if round or 
oval, highly refractile bodies are seen, they should be 
stained for spores. 
According to Fischer motile bacteria always come to 
a state of rest or immobility previous to spore-forma- 
tion. Several species first become elongated. The 
anthrax bacillus does this, and a description of the 
method of its production of spores may serve as an 
illustration of the process In the beginning the pro- 
toplasm of the elongated filaments is homogeneous, 
but after a time it becomes turbid and finely granular. 
These fine granules are then replaced by a smaller 
number of coarser granules, which are finally amalga- 
mated into a spherical or oval refractile body. This 
is the spore. As soon as the process is completed there 
appears between two spores a delicate partition wall. 
For a time the spores are retained in a linear position 
by the cell membrane of the bacillus, but this is later 
dissolved or broken up and the spores are set free. 
Not all the cells that make the effort to form spores, 
as shown by the spherical bodies contained in them, 
bring these to maturity; indeed, many varieties, under 
certain cultural conditions, lose their property of forming 
spores. The following are the most important spore 
types: (a) The spore lying in the interior of a short 
undistended cell ; (b) the spore lying in the interior of 
a short undistended cell forming one of the elements of 
a long filament : (¢) the spore lying at the extremity 
of an undistended cell much enlarged at that end—the 
so-called ‘‘ head spore ;’’ and (d) the spore lying in 
