46 BACTERIOLOGY. 



remain attached because of the incompletely divided cell- 

 wall, diplococci, streptococci, tetrads, sarcines and staphy- 

 lococci may result. As a rule, a given micrococcus shows 

 some one of these six forms as its characteristic form. 

 Thus, a micrococcus that forms a streptococcus will not 

 occur as a tetrad or as a sarcine. 



FIG. ii. Division forms of the spirillum, a Vibrio, b 

 cell, form of elongated S; c Long spirillum, showing compraa , 



cells. 



The spiral or screw-shaped bacteria multiply by trans- 

 verse division, as in the case of bacilli. When the organ- 

 ism grows single it forms a bent and twisted rod which, as 

 ordinarily seen, appears comma-shaped. The comma 

 bacilli, or vibrios, are the individual cells which, when they 

 remain attached, end to end, yield a spirillum (Fig-. 11). 

 The spirillum,- therefore, may be considered as analogous 

 to the thread, and streptococcus. Certain spirilla, like 

 those of the mouth and of recurrent fever, cannot be 

 resolved into, component cells, and are therefore to be 

 considered as single individuals. 



Spores. 



It has been pointed out above that bacteria always 

 multiply by division. In this process one cell, dividing 

 into two halves, yields two new individuals. As long- as 

 the organism is growing and multiplying it is said to be 

 vegetating and the form which it presents during this 

 period of its life is spoken of as the vegetative form. 

 This stage, therefore, may be compared to the growing, 

 higher plant. The latter, however, when it reaches the 

 adult condition develops reproductive organs and forms 

 seeds. 



