156 BACTERIA. 



4. — Different foi'ins of Bacteria are classed under this heading. 

 When they occur alone, they may be either spherical, as in certain 

 forms of Micrococcus, or rod-like, as in the true Bacteria. When 

 they occur aggregated together, they may be of the form of rudi- 

 mentary cells, as in other varieties of micrococcus, or as rod-like 

 structures joined together. Even this last arrangement admits of 

 sub-division, as rod-like parts may be conjoined end on end, or at 

 an angle (not of 180°), or wound in a spiral. The following table 

 may make this clear : — 



T 1 1- h4 Spherical — ^.^., Micrococcus. 



\ Rod-like — e.g.^ Bacterium. 

 r^ /Spherical — ^.^., Micrococcus. 



-r, J i^ I , Parts joined endonend^.p., Bacillus. 



Bacteria./ •?: < / •' ^ i at-u • 



5 i Rod-like " " ^^ ^^ angle— ^.^., Vibrio. 



\ ^ !' " spirally (often a double 



I spiral) e.g.^ Spirillum and 



^ Spirochsete. 



5. — Effects of Re-agents and Temperature. 



(a) Iodine stains all formative matter or protoplasm brown, and 

 occurs with all formative matter, ready to be, but not yet actually 

 transformed into a plant or animal substance. The outer wall 

 does not stain. 



(/3) Magenta or carmine solution also stains protoplasm, 



(r) A temperature of o" C. (32 F.) and of 60^ C. (140^ F.) 

 kills them. These are their limits of temperature. They thrive 

 best at 30 C.^ (86^ F.). 



(^) Dessication. They can survive a lengthy period of drying 

 or dessication, and on adding moisture they revive. 



{b) Digestion. — Bacteria feed on decaying organic matter. 

 Hence their name of Saprophytes (ca-n-pog — putrid, (pvTov — plant). 

 Pasteur's fluid causes them to thrive. This food is taken in by 

 the whole of the general surface. There is no definite mouth or 

 digestive apparatus. 



(c) Absorption. — As in many of the lower living beings, the 

 function of absorption is merged with that of digestion. The 

 whole surface of the Bacteria absorbs food. But that very 



