The Preservation of Health 



287 



be roughly divided into groups, according as they are 

 spherical, rod-like, or spiral in shape. The term bacillus is 

 usually restricted to rod-shaped bacteria. 



Bacteria are propagated in a very simple manner. Usu- 

 ally the parent cell divides into two ; these two into two 

 others, and so on. Under certain conditions, however, 

 bacteria reproduce 

 themselves by 

 spores which are 

 formed in the inte- 

 rior of cells and 

 then passed out. 

 These spores are 

 much more tena- 

 cious of life and 

 therefore are much 



FIG. 156. Various Forms of Bacteria. (Drawn 

 from photographs.) 



A, spheroidal bacteria (called cocci} in pairs ; J5, same 

 kind of bacteria in chains ; C, bacteria found in pus 



(grouped in masses like a bunch of grapes). (Bacteria 

 in A, B, and C magnified about 1000 diameters.) 

 Z>, bacteria found in pus (tendency to grow in the 

 form of chains). (Magnified about 500 diameters.) 



harder to destroy 

 than the fully de- 

 veloped cells. The 

 rapidity with which bacteria multiply under favorable con- 

 ditions makes them, in some cases, dangerous enemies 

 to plant and animal life. 



446. General Action of Bacteria. Bacteria have the 

 power of bringing about decomposition of various kinds. 

 Thus, as we have learned in a previous chapter, a highly 

 organized fungus, like the yeast plant, growing in the 

 presence of sugar, has the power of breaking down this 

 complex body into simpler ones, viz., alcohol and carbon 

 dioxide (see Experiment 29). 



In the same way various forms of bacteria have the 

 power of breaking down complex bodies, the products 

 depending upon the substance, the kind of bacteria, and 

 the conditions under which they act. Thus, the bacteria 



