36 BACTERIOLOGY. 



its division into two cells it becomes elongated and ap- 

 pears as a 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 us in 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 Q.3/J. 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 have elongated or lancet- 



