BACTERIA IN NATURAL PROCESSES. 119 



or free nitrogen. Even his nitrates may be thus 

 lost by bacterial action. This portion is lost to 

 the farmer completely, and he can only hope to 

 replace it either by purchasing nitrates in the 

 form of commercial fertilizers, or by reclaiming it 

 from the air by the use of the bacterial agencies 

 already noticed. With the knowledge now at his 

 command he is learning to prevent this waste. 

 In the decomposition one large factor of loss is 

 the ammonia, which, being a gas, is readily dis- 

 sipated into the air. Knowing this common re- 

 sult of bacterial action, the scientist has told the 

 farmer that, by adding certain common chemic- 

 als to his decomposing manure heap, chemicals 

 which will readily unite with ammonia, he may 

 retain most of the nitrogen in .this heap in the 

 form of ammonia salts, which, once formed, no 

 longer show a tendency to dissipate into the air. 

 Ordinary gypsum, or superphosphates, or plaster 

 will readily unite with ammonia, and these added 

 to the manure heap largely counteract the tend- 

 ency of the nitrogen to waste, thus enabling the 

 farmer to put back into his soil most of the nitro- 

 gen which was extracted from it by his crops 

 and then used by his stock. His vegetable crops 

 raise the nitrates into proteids. His animals feed 

 upon the proteids, and perform his work or fur- 

 nish him with milk. Then his bacteria stock 

 take the excreted or refuse nitrogen, and in his 

 manure heap turn it back again into nitrates 

 ready to begin the circle once more. This might 

 go on almost indefinitely were it not for two 

 facts : the farmer sends nitrogenous material off 

 his farm in the milk or grains or other nitro- 

 genous products which he sells, and the de- 

 composition processes, as we have seen, dissi- 



