Structure, Growth and Distribution. 3 



Size of bacteria. All of the bacteria are so small they 

 n not be seen by the unaided eye. In fact their min- 

 uteness is such as to render difficult any adequate con- 

 ception of their size. In a single teaspoonful of sour 

 cream ready for the churn, there are often 1,500.000,000 

 bacteria. The teaspoonful of cream is not more 

 crowded than is our world with the 1,500,000,000 peo- 

 ple living on its surface. In the drop of cream each 

 organism is living its own life and doing a certain 

 amount of work as is each person on the surface of the 

 globe. 



The different kinds of bacteria vary considerably in 

 relative size. The largest may be several hundred times 

 as large as the smallest forms. Even with the largest, 

 one hundred or more laid side by side would not equal 

 in thickness an ordinary sheet of paper. 



Manner of reproduction. Most of the ordinary plants 

 increase in number by forming seeds. The seed ger- 

 minates and grows into a plant which may produce 

 thousands of seeds similar to the one planted. Many 

 kinds of fungus plants reproduce by the formation of 

 spores, which in some ways are analogous to the seeds 

 of the higher plants. The cloud of smoke from the ripe 

 puffball is made up of its tiny spores. The ripe smut 

 on the corn owes its black color to the multitude of 

 spores it contains. 



In their manner of reproduction the bacteria are to 

 be compared to the individual cell of the higher plant 

 or animal rather than to the entire plant. The germi 

 nating corn plant is made up of a number of cells. 

 These divide each into two, these two cells again divide 

 to form four cells and so on, the plant, meanwhile, in- 



