SHAPE AND ARRANGEMENT OF &ACILLI 33 



which has given rise to a subdivision of the cocci into several 

 groups. 



Subdivision of Cocci. Cocci, after the first division, may adhere to 

 each other, but after the second division usually separate, generally 

 forming in groups of two, called diplococci. They may, however, 

 adhere together until after the second division, in which case they 

 form groups of four, called tetrads (tetra Greek word for four). 

 Again they may divide in all three directions of space and adhere 

 together, then we obtain square packages of cocci called sarcina. 

 Yet, again, division may be in one direction only, when there are 

 formed regular rows or chains or cocci, called streptococci (chain- 

 cocci). Finally, the division of the cocci may go on in an irregular 

 manner in all three dimensions of space, resulting in the formation 

 of irregular clusters, resembling bunches of grapes, which are called 

 staphylococci. f 



FIG. 19 



Varieties of spherical forms: a, tendency to lancet-shape; 6, tendency to coffee-bean shape; 

 c, in packets; d, in tetrads; e, in chains; f, in irregular masses. X 1000. (After Flugge.) 



Classification of Cocci. The single coccus, or micrococcus. 



The diplococcus, or group of two cocci. 



The tetrad, or group of four cocci. 



The sarcina, or cuboidal (dice-like) group of eight or sixteen or 

 more cocci. 



The staphylococci, or several cocci irregularly arranged like a 

 bunch of grapes. 



The streptococci, or a group of several cocci arranged like a row of 

 beads (chain cocci). 



Shape and Arrangement of Bacilli. Bacilli shows varying features 

 as to details of shape. Some are quite slender, others plump, thick, 

 and short. Some of them, like the anthrax bacillus, are cylindrical, 

 straight, and stiff, with square ends, while others show rounded ends, 

 like the typhoid, colon, and hog-cholera bacilli. There are bacilli 

 which are pointed at one end and club-shaped at the other, or club- 

 shaped at both ends, like the diphtheria and glanders bacilli. Again, 

 others, instead of being straight, are often slightly but distinctly 

 curved like the tubercle bacillus. Certain bacilli, as the anthrax, 

 3 



