BACTERIA. 



The excretions of the bacteria in milk, fish, etc,, 

 may produce changes which, very apparently, ren- 

 der them unfit for food, or the changes may not be 

 apparent. If food containing these excretions be 

 eaten, or if the bacteria grow in the body itself, the 

 excretions may bring about abnormal conditions more 

 or less severe, but all may be called disease. 



Like the mag- 

 gots in cheese or 

 the clothes moth 

 larva, the bacteria 

 live surrounded by 

 their food supply 

 and they have only 

 to take, digest, and 

 absorb it as need- 

 ed. Like these animal forms, they feed upon com- 

 plex organized food which has been previously pre- 

 pared by other plants or animals. In this they differ 

 from most plants which must manufacture their food 

 out of the mineral and other inorganic substances in 

 air, water, or soil. However, some species can do 

 this although they have not the green coloring mat- 

 ter or chlorophyll cells which in the higher plants are 

 the food factories. 



Because of this power of living on inorganic sub- 

 stances, which no known animal possesses, the sci- 

 entists have decided that these micro-organisms must 

 be called plants rather than animals. 



Bacteria have no leaves, roots, stems, or any or- 



A BACILLUS DIVIDING INTO 

 TWO GENERATIONS. 



