104 



CLASSIFICATION OF PLANTS 



dation into nitrates. These bacteria and others are holophytic, assimilating 

 carbon dioxide Hlce green plants. Bcggiatoa alba grows in water where 

 there is sulphuretted hydrogen, HoS, formed by the decomposition of 

 organic matter. The bacterium causes the oxidation of the HoS whereby 

 the sulphur is set free and deposited in the cell in small granules. Lepto- 

 thrix ochra?a oxidizes iron carbonate into iron oxide (iron ore) which 

 is likewise deposited in the cell. 



230. Through the ferments formed by many bacteria sugar is formed 

 from starch and the sugar is then split into alcohol and carbon dioxide, 

 C6HijOf,= 2C-H60+2C02. This is the common type of fermentation 

 which takes place in the making of bread, wine, beer and other alcoholic 



Fig. 61. — Staphylococcus aureus. (Williams.) 



fluids. Another common type of fermentation is produced by the Bacillus 

 vulgaris and other bacteria. The process here is ordinarily spoken of as 

 decay. Nitrogenous substances, like flesh, are decomposed and, among 

 other products, sulphuretted hydrogen is set free. It is this gas which 

 produces the evil odor so characteristic of this type of bacterial activity. 



231. Among the parasitic bacteria are some which cause little or no harm 

 to the host. Some may even be useful, as when those inhabiting the 

 digestive tract assist in the process of digestion (Bacillus coli communis). 

 But again others may be the cause of the most malignant and contagious 

 diseases. Species of Streptococcus and Staphylococcus are generally 



