98 ELEMENTS OF AGRICULTURE 



ure an inch. Of the very smallest ones, it takes about 150,- 

 000 to measure an inch. The small size of the bacteria 

 is more than made up by the rapidity with which they 

 multiply. They reproduce by sim- 

 ple division, one individual divides 

 into two. This division may take 



Fio. 48. The point of the 



finest cambric needle. A par- place every fifteen to thirty min- 



ticle of dust above the point 



and a mass of bacteria below. uteg un( J er favorable Conditions. 



If each divider into two every quarter of an hour, there 

 will be an immense number of them at the end of a 

 day, even if there were only one in the morning. The 

 limit of food supply and other conditions prevent this 

 rapid multiplication from continuing. 



Bacteria of many kinds are present in all soils, ranging 

 from less than 28,000,000 per ounce of soil to many times 

 this number. In fertile soils like gardens there are many 

 billions per ounce. In a fertilizing experiment in New 

 Jersey it was found that the plots that gave the greatest 

 yields of asparagus also contained most bacteria. Often 

 there is a relationship between the number and kind of 

 soil-bacteria and fertility. 



Bacteria may seem to be too small to be of much con- 

 sequence, but they are far from unimportant. We know 

 how many contagious diseases are caused by bacteria, 

 so that we must recognize their power. Perhaps you have 

 come to look upon all bacteria as harmful, things to 

 be avoided. But, while certain ones cause tuberculosis, 

 diphtheria and lock-jaw, many other kinds are useful 

 to us. Bacteria are microscopic plants. We should look 

 on them as we do on other plants. Some plants, as corn 

 and cotton, are useful; others, like poison ivy, are to be 



