28 VETERINARY BACTERIOLOGY 



reproduction of the more usual or normal type when brought 

 under favorable conditions. Frequently, however, these cells 

 soon die and can no longer reproduce. Various bacteria differ 

 considerably with respect to the ease with which they produce 

 involution forms. 



Grouping of Bacterial Cells. The cells of bacteria are frequently 

 surrounded by a gelatinous material (capsule, see below) which 

 causes them to cling together in groups. This grouping in the 

 various types is so constant that it is used to differentiate various 

 genera from each other, and in some cases the species within 



Q Q CSXD COCO OC36C56OOO 



Q 4 G 



O O> GG 



4D OQ 



Fig. 4. Development of groups of cocci: 1, Development of strepto- 

 coccus; 2, development of micrococcus; 3, development of sarcina; 4, 

 development of staphylococcus. 



the genus. Bacterial cells divide normally at right angles to the 

 longest axis of the cell. This allows of but little variation in the 

 grouping of elongated types, but as the cocci have no " longest 

 axis" they divide in various planes. 



Some cocci divide constantly in the same plane or in a plane 

 parallel to the first. This results in the formation of a chain 

 of cocci. An organism showing this grouping is culled a strepto- 

 coccus (pi. streptococci). 



other cocci divide alternately in two planes at right angles 

 to each other. Such an organism will be found in twos (diplo- 

 eoccus) or in fours (tetrad or tetracoccus) . Diplococci may also 



