CHAPTER LXXVII. 



B A C T E E I A. 



Bacteria, a division ui the smallest aud simplest of plants 

 — rounded, ovoid, or spiral in shape — are unicellular and de- 

 void of chlorophyll. They consist of protoplasm enclosed in a 

 membrane, having a great affinity for certain stains, and are, 

 in common with vegetable matters, not destroyed by potash, 

 ammonia, or weak acids, and have the power of reproduction, 

 some also of movement. They are divided into four great 

 classes, each of which is recognised by the shape and size of its 

 individuals, and also sometimes by their method of growth. 



I. Spherobacteriens, very small, rounded or ovoid in shape, and 

 may be either micrococci or monads. If the latter, which 

 are believed to be spores, they may be traced growing 

 into tubules ; if micrococci, the globular form remains. 

 II. Microbacteriens, large rod-shaped, and may be bacteria or 

 bacilli. If bacteria, they remain short ; if bacilli, they 

 may grow into lengthened filaments, having rounded 

 cells — vspores. These rods vary in shape ; some are 

 swollen in the middle, some pisiform, swollen in the 

 middle and attenuated at the ends ; others constricted in 

 the middle, as Baderiens termo ; and some enlarged at 

 one end — club-like. They are again divided into three 

 groups — (a.) coloured bacteria, found in ovine milk, &c. ; 

 (&.) zymotic ; and (c.) pathogenic bacteria. 



III. Dcsmohacteriens. 



IV. Spirobaderiens. 



Bacteria have been carefully measured, aud the results are as 

 follows : — 



Length. Breadth. 



Bacteria, . . . 2 to 5 mill. 6 to 1"7 mill. 



„ termo, 

 Bacilli anth. 



,, iilva, 

 Spu-illi, 

 Micrococci, 



3 „ 8 „ 6 „ -8 



10 „ 50 „ 1 „ 2-0 



5 „ 8 „ -7 „ 1-0 



10 „ 40 „ 7-0 



— -5,, 1-0 



