18 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



crosswise, must occur eith'er as isolated cells or in chains. 

 Such an organism is sometimes termed a streptoiacUlus. 

 Spiral bacteria very rarely occur in groups though occasion- 

 ally they are found in chains. 



It has been stated that bacteria always divide at right 

 angles to the longest axis of the cell. Spherical cells, or 

 cocci, have no longest axis. There is, therefore, a priori no 

 reason why they cannot divide in any plane. Some spheri- 

 cal cells show no regularity in the manner in which they 

 divide. If such cells cling together they will form an irreg- 

 ular or grape-clusterlike mass. Such an organism is termed 

 a staphylococcus. Some cocci show a decided tendency to re- 

 main united in pairs. An organism of this type is termed 

 a diplococcus. When spherical cells divide persistently 

 in parallel planes a chain of cocci will be produced. Such 



a 



@ 



Fig. 3. — -Forms and grqupings or thf cocci. 1. Single or isolated 

 cells. 2. Irregular masses. 3. Pairs. 4. Chainp. 5. Plates. 6. 

 Packets or cubes. 



an organism is termed a streptococcus. A few kinds of 

 cocci have been described which divide alternately in two 

 planes forming first pairs, and then squares of' cells. An 

 organism of this type may be termed a pediococcus. Still 

 others divide in three planes, each plane at right angles to 

 the other two. This will result in the formation first of 

 pairs, then of squares, then of cubes of bacteria. Such a 

 cubical collection of bacteria is termed a sarcina. 



It should be noted that the names given above are not the 

 scientific names of genera, but are common descriptive 

 terms. It will be found later that some of these same words 



