46 _ BACTERIOLOGY. 
other as single cells, the tendency then is for the seg- 
mentation to be incomplete, the cells remaining together 
in masses. The indentations upon these masses or 
cubes, which indicate the point of incomplete fission, 
give to these bundles of cells the appearance commonly 
ascribed to them—that of a bale of rags. As already 
said, division in two opposite directions results in the 
formation of a group of forms as tetrads. Division 
irregularly in all directions results in the production 
of ‘clusters. The rod-shaped bacteria never divide 
longitudinally. 
Spore-formation must be distinguished from vegeta- 
tive reproduction. This is the process by which the 
organisms are enabled to enter a stage in which they 
resist deleterious influences to a much higher degree 
than is possible for them in the growing or vegetative 
condition. There are two kinds of spores which have 
been described: 1. Endospores, which are strongly 
refractile and glistening in appearance, oval or round 
in shape, and developed within the interior of the cell. 
They are characterized by the power of resisting to a 
considerable extent the injurious influences of heat, 
desiccation, and chemical disinfectants. 2. Arthro- 
spores, or jointed spores, developed not within the cell 
but as a sprout like separation of one of its extremi- 
ties. These jointed bodies are believed by some to 
have also greater resisting power to desiccation, etc., 
than the ordinary cells, though less than the endo- 
spores, and to serve the purpose of reproductive 
elements. Recent researches into the formation of 
arthrospores, however, have resulted in nothing defi- 
nite, and the question of their existence even in bac- 
teria still remains open. In describing the biological 
