PRACTICAL BACTERIOLOGY. 



If certain plants, preferably some green Algae, sucli 

 as Spirogyra, Vaucheria, or Cladophora, are left for 

 a short time in a small quantity of water, so that 

 they become decomposed, one very soon perceives, 

 by the unpleasant odour produced, that bacteria have 

 begun their destructive processes. The water be- 

 comes turbid, and the sides and bottom of the vessel 

 become covered with a slimy film, which grows 

 thicker and thicker, till at last here and there small 

 flakes become detached from the rest. Sooner or 

 later, according to the temperature, the surface be- 

 comes covered with a dirty white skin, which at first 

 is very delicate, but which frequently, later on, be- 

 comes of a gelatinous consistency. The turbidity of 

 the water, the slimy covering of the vessel's walls, 

 and the skin on the surface (the bacterium skin), all in- 

 dicate the presence of bacteria, which have multiplied 

 in enormous quantities at the expense of the dying 

 Algse. The bacteria were originally present in pro- 

 portionately a small quantity, both in the water and 

 attached to the Algse themselves and to the walls of 

 the vessel. 



Similarly bacteria can easily be obtained for exami- 

 nation by cutting up carrots or potatoes, boiling them, 

 and allowing the resulting liquid to stand in broad 

 open vessels. Essentially the same appearances mani- 

 fest themselves as with the decomposing Algse, only 

 as a rule not nearly so many species are obtained. 



