22 MORPHOLOGY OF BACTERIA. 



Another equally plausible explanation is that it is a sprout 

 from one end of the cell, or a constriction ; but this definition 

 is not so satisfactory as that of Hueppe. 



Whenever spore-formation is referred to, the endogenous 

 spore (endospore) is meant unless the other variety is men- 

 tioned specifically. 



CLASSIFICATION : It is rather difficult to classify bacteria 

 properly. In order to include all the varieties and species, 

 several classifications must be made. 



First, as to their shape, we have three principal divisions 

 or groups : micrococci, bacilli, and spirilla. 



The micrococci (Fig. 5) are spherical or slightly oval in 



FIG. 5. 



o_ a. 



a. Staphylococci. 6. Streptococci, c. Diplococci. d. Tetrads, e. Sarcinse. 

 (Abbott.) 



shape, non-motile, and do not form spores. They grow by 

 binary division. This group is subdivided further into the 

 following varieties : 



Diplococcus : two micrococci remaining attached to each 

 other, or an imperfect division. They may be absolutely 

 spherical or the contiguous surfaces may be slightly flattened 

 or concave, the "biscuit" coccus or " semmelkokken." 



Tetrad: a group of four cocci, the result of division in two 

 directions. 



Sarcina : a packet or cube of eight cocci, the result of divi- 



