36 BACTERIOLOGY. 
its division into two cells it becomes elongated and ap- 
pears asa short oval rod; at the moment of its division, 
on the contrary, the transverse diameter of each of its 
two halves is greater than their long diameter. A 
short rod becomes in the same way, at the moment 
of its division, two cells, the long diameter of each of 
which may be even a trifle less than its short diameter, 
and thus they appear on superficial examination as 
spheres. 
As bacteria multiply the cells produced from the 
parent cell have a greater or less tendency to remain 
attached. In some varieties this tendency is extremely 
slight, in others it is marked. This union may appear 
simply as an aggregation of separate bacteria or so close 
that the group appears as a single cell. According to 
the method of the cell division and the tenacity with 
which the cells hold together, we get different group- 
ings of bacteria, which aid usin their differentiation and 
identification. Thus whether the bacterial cell divides 
in one, two, or three planes, we get forms built in 
one, two, or three dimensions. If we group bacteria 
according to the characteristic form of the cells, and 
then subdivide them according to the manner of their 
division in reproduction and the tenacity with which 
the newly developed cells cling to one another, we will 
have the following varieties : 
1. Spherical Form, or Coccus (Figs. 1 to 4). The size 
varies from about 0.34 as minimum diameter to 3 as 
maximum. The single elements are at the moment of 
their complete development, so far as we can deter- 
mine, absolutely spherical; but when seen in the process 
of multiplication through division the form is seldom 
that of a true sphere. Here we bave elongated or lancet- 
