58 BACTERIA AND SOIL FERTILITY 



made use of by the chemist in separating nearly related com- 

 pounds. Numerous bacteria utilize alcohol and one class obtains 

 its energy from it and yields the valuable by-product, vinegar. 



The carbon in the fat molecule is more resistant to the attack 

 of bacteria. For this reason it often gives considerable trouble 

 to the plumber. Fatty materials are thrown into the sink, they 

 find their v^ay into the sewer, bacteria dissolve the accompanying 

 substances and the fat is liberated. This collects around some 

 object, as for instance a match. As this is rolled along by the 

 water it gathers more fat, until at times it becomes large enough 

 to clog a pipe. Proteins yield their carbon readily and often in 

 the breaking of them down, as for example in the egg, the sulfur 

 is changed to the ill-smelling gas, hydrogen sulfide. A few of 

 the pathogens require their carbon as the complex body tissues and 

 fluids, and a very few at the present time seem to require that 

 this tissue or fluid be in the body of a living animal. 



Nitrogen. — Nitrogen in the free form is one of the lazy ele- 

 ments. However, when once cajoled into joining hands with 

 carbon and oxygen we get our most wonderful compounds. The 

 most beautiful dyes contain nitrogen. It is tucked away in our 

 most powerful explosives, ready on the least provocation to be- 

 come excited and blow everything to pieces. The most delicate 

 perfumes and powerful poisons contain it. But most wonderful 

 of all, it is the basis of living protoplasm. All microorganisms 

 require it in one form or another. The nitrogen-gathering or- 

 ganisms of the soil can cause the lazy atmospheric nitrogen to 

 join hands with carbon, hydrogen, and oxygen and thus produce 

 their mysterious body. There are bacteria in the manure which 

 will transform urea into ammonia. Another class of organisms 

 oxidize the ammonia to nitrites; still others, in getting their 

 energy, transform the, nitrites into nitrates. Many bacteria can 

 use the nitrogen in egg, milk, flour, and all kinds of plants and 

 animal tissue; others require a complex nitrogen compound of 

 living plant and animal tissue. Sometimes the protein compounds 

 are pulled to pieces with the formation of ptomains; at other 

 times they are built into those most powerful of all poisons, 



