20 THE STORY OF GERM LIFE. 



tococcus, and all which divide in three division 

 planes form another genus, Sarcina, etc. 



FIG. 5. Sarcina. 



FIG. 6. Separate rods 

 showing variations in 

 size, magnified about 

 looo diameters. 



The rod-shaped bacteria also differ somewhat, 

 but to a less extent. They almost always divide 

 in a plane at right angles to their longest dimen- 

 sion. But here again we find some species sepa- 

 rating immediately after division, and thus always 

 appearing as short rods (Fig. 6), while others 



remain attached 

 after division 

 and form long 

 chains. Some- 

 times they ap- 

 pear to continue 

 to increase in 

 length without 

 showing any 

 signs of divis- 



FIG. 7. Rod-forms united to form chains, ion, and in this 



way long threads 



are formed (Fig. 7). These threads are, however, 

 potentially at least, long chains of short rods, and 

 under proper conditions they will break up into 

 such short rods, as shown in Fig. 7 a. Occasion- 

 ally a rod species may divide lengthwise, but this 

 is rare. Exactly the same may be said of the 



