THE WORLD OF MICROSCOPIC LIFE 53 



four hours would be about a fortieth of a cubic 

 millimeter; after two days the volume would be 

 about a half liter or about one pint; and after four 

 and a half days, however, the volume would more 

 than equal that of the water of the entire Pacific 

 Ocean ! 



The food material utilized by bacteria varies 

 with different species. A few forms are able to 

 build up their living substance out of purely min- 

 eral constituents. One of the sulphur bacteria can 

 subsist on a bill of fare made up as follows: 



Here we have the food supply reduced to perhaps 

 its simplest possible terms. Most kinds of bac- 

 teria, however, demand some organic matter. A 

 great many species live upon compounds furnished 

 by the dead bodies of plants and animals whose 

 decomposition is brought about by the activity of 

 these minute forms. The large number of para- 

 sitic bacteria which subsist within the bodies of 

 plants and animals are still more specialized in 



