CLASSIFICATION 



75 



plants can assimilate carbon-dioxide, and these Bacteria manufac- 

 ture all of their organic substances from inorganic compounds. 

 The greater number of Bacteria are saprophytes, feeding on dead 

 organic matter, whose decomposition is due to their presence. Others 

 are true parasites, and are the causes of disease in both plants and 

 animals. 



Holophytic Bacteria. The holophytic Bacteria, i.e. those which, 

 like green plants, are independent of organic food, are few in num- 

 ber, and all known forms belong to the Nitrogen Bacteria. These 

 forms are capable of assimilating carbon-dioxide, but this power is 

 not dependent on the presence of light, as it is in green plants. 



Fia. 52. Micrococcus polypus. Plate-culture, eight days old (xb). (AfterMiQULA.) 



Saprophytic Bacteria. Bacteria are the principal agents in organic 

 decomposition, and it is here that their enormous importance in the 

 economy of nature is most evident. That Bacteria are the direct cause 

 of decomposition is very simply shown by the behavior of dead 

 organic substances when they are protected from the attacks of 

 Bacteria. This is practically demonstrated in all the devices em- 

 ployed for preserving organic substances from decay. Fruit, meat, 

 etc., are subjected to a temperature sufficient to kill all bacterial 

 germs which may be present, and then hermetically sealed so as to 

 prevent access of germs from without. If this is successfully done, 



