34 BACTERIA AND THEIR PLACE IN NATURE 



character of food the bacteria find in the soil. If the soil is rich in 

 plant residues barnyard manures and the like many bacteria will 

 be found there pulling these substances to pieces, liberating gases 

 and acids which act upon insoluble particles of the soil and render 

 them soluble. One class of organisms changes the protein constitu- 

 ents of the soil into ammonia. This type is called " ammonifiers." 

 A person can often detect their activity from the odor of ammonia 

 coming from manure heaps. 



Most plants cannot, however, use nitrogen in the form of ammonia; 

 it must be in the form of nitrates. This transformation is brought 

 about by two distinct types of organisms. One of them feeds upon 

 the ammonia produced and manufactures nitrous acid. Should the 

 change cease at this point and nitrites accumulate in the soil in 

 large quantities, plants would not grow upon it, for this is a poison 

 to plants. But in soils properly cared for only minute quantities 

 of nitrites accumulate. As soon as they are formed another type 

 of organism feeds upon them and manufactures nitric acid for the 

 growing plant. This, when formed, reacts with other constituents 

 of the soil, such as limestone. It is then ready to be taken up by the 

 plant and manufactured into nourishing food, beautiful flowers, or 

 fragrant perfumes for the human family. 



Were it not for bacteria the world in time would be filled with 

 never-changing organic matter. The plant residues, trees, and 

 animal bodies would remain stored up in the soil, and with it that 

 element carbon which, in the form of carbon dioxid, is required 

 by all chlorophyl plants. Bacteria, in getting the energy which they 

 require in their life activity, are continually liberating carbon so 

 that it may start again on its journey of construction. If carbon 

 and nitrogen could but speak, what tales of wonderment they would 

 tell ! The chemist, the bacteriologist, and the farmer would each be 

 wiser, for many of the changes through which carbon and nitrogen 

 pass, due either to the action of the lower plants bacteria or that 

 of the higher plants are so complex that even the scientist with his 

 apparently magical methods cannot follow them. 



So far only the plant-food in the soil and the changes through 

 which it passes have been considered. The farmer, however, is 

 usually more concerned with that substance his soil lacks and which 

 must be supplied in order to get good crops. In many cases the 

 lacking element is nitrogen. One notes from the fertilizer quotations 

 that the elements will cost fifteen cents a pound or over if purchased 

 in the form of sodium nitrate, ammonium sulfate, or dried blood. 

 If one stops to make a simple calculation he finds that it would cost 

 fifteen dollars for enough to produce 100 bushels of corn, eleven 

 dollars for enough to produce 50 bushels of wheat, and seven dollars 

 and fifty cents for enough to produce one ton of alfalfa hay. In 

 these calculations it has been assumed that one could get back in 



