26 PRINCIPLES OF BACTERIOLOGY 



even a trifle less than its short diameter, and thus they appear on super- 

 ficial examination as spheres. 



As bacteria multiply the cells produced from the parent cell have 

 a greater or less tendency to remain attached. This is on account of 

 the slimy envelope which all bacteria have more or less developed. 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 groupings 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 : 



FIG. 2 



:::: . 



:::: * 



r/ 







^nn 



Varieties of spherical forms : a, tendency to lancet-shape ; b, tendency to coffee-beau shape ; c, in 

 packets ; d, in tetrads ; e, in chains ; /, in irregular masses. (After Fliigge.) 



1. SPHERICAL FORM, OR Coccus (Fig. 2). The size varies from 

 about 0.3/J. as minimum diameter to 3/* as maximum. The single 

 elements are at the moment of their complete development, so far as 

 we can determine, 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-shaped forms, as frequently 

 seen in the diplococcus of pneumonia, or the opposite, as in the diplo- 

 coccus of gonorrhoea, where the cocci appear to be flattened against 

 one another. Those cells which divide in one direction only and remain 

 attached are found in pairs (diplococci) or in shorter or longer chains 

 (streptococci). Those which divide in two directions, the one at right 

 angles to the other, form bunches of four (tetrads). Those which 

 divide in three directions and cling together form packets in cubes 

 (sarcinre). Those which apparently divide irregularly in any axis 

 form irregularly shaped, grape-like bunches (staphylococci). 



There are a considerable number of bacteria which appear to fre- 

 quently assume spherical forms, or at least forms so like spheres that 

 they cannot be differentiated from them, and yet under other conditions 



