i62 DISEASES DUE TO BACTERIA 



DISEASES DUE TO BACTERIA. 



GENERAL FEATURES OF BACTERIA. 

 (After E. W. Hey Groves.) 



GENERAL CHARACTERS. 



Fission fungi. Devoid of chlorophyl. Unicellular vegetable 

 organisms. Consist of protoplasm surrounded by a cell wall. 



REPRODUCTION. 



(a) By simple fission. — The common method. 



(b) By Spore formation. — Only found in a few bacilli. 

 Never found in common pyogenic bacteria. 



Occurs, e.g., in B. anthracis, B. tetani, B. cx^dematis maligni. 



Spores are formed when conditions for bacterial life are un- 

 favourable. They have a thick capsule, and are very 

 strongly resistant to desiccation, heat, or antiseptics. 



(c) By budding, e.g., yeast. 



LOCOMOTION. 



Passive. — By Brownian movement, physical or chemical currents. 

 Active. — By flagelUe, i.e., actively contractile protoplasmic 



processes. 



Found in B. typhosus and B. coli. 



SHAPE. 



Cocci. Round; never produce spores. Gram + 

 Staphylococci ; arranged irregularly. 

 Diplococci ; arranged in pairs. 

 Streptococci ; arranged in chains. 

 Tetracocci ; arranged at four corners of a square. 

 Sarcin^e ; B. arranged at eight corners of a cube. 

 Bacilli. Rod shaped, often spore-bearing. Gram + and — . 

 Streptobacilli ; chains of bacilli. 

 Leptothrix; long threads. 

 Spirilla; spirally curved. 



PHYSIOLOGY. 



They require organic proteids for food because they have no 

 chlorophyl. 



Parasites obtain it from living animals or plants. 



Saprophytes obtain it from dead tissues. 



Facultative parasites ordinarily live on dead tissues, but can also 

 grow in living, e.g., B. proteus. 



