Biological Papers. 205 



may be reduced to a usable condition. Among these bacteria are : 

 fUicillius colli, B. mycoides, B. mesentericus, B. liquidu.s, B. pro- 

 digiosus, B. ramof^is, B. vermiciilai'is, B. liquefaciens and many 

 members of the great family of Pioteus. 



2. The air-hating, denitrifying bacteria are responsible for the 

 more or less complete destruction of the nitrates in the farm and 

 commercial fertilizers, when these are buried in such a way that air 

 is largely excluded. They also do an important work in assisting 

 the bacteria of putrefaction in destroying excrement in cesspools 

 and retention vats, where sewage is detained for work of this char- 

 acter. These bacteria work best where the supply of air is limited 

 and the amount of organic matter great. The organic matter is 

 oxidized with oxygen taken from the nitrates, and a distinct rise of 

 temperature results, as may be seen in heaps of manure. Much 

 nitrogen, consequently, is lost to the manure and soil. Among the 

 denitrifying bacteria that have been isolated are: Bacillus flvor- 

 escens rion-liquefaciens, Mycoderma urece, and some of the Staphy- 

 lococci. 



The very effective character of the work done by the putrefactive 

 and denitrifying bacteria was proved by the late Colonel Waring, 

 the eminent sanitary engineer. He kept two tons of dry earth for 

 use over and over in dry-earth closets. The closets were emptied 

 once in two months in heaps on the floor of a dry cellar. This 

 material was used, in all, about ten times, and then the material 

 was analyzed for the amount of nitrogen it contained. It was found 

 that 4000 pounds of the soil had only eleven pounds of nitrogen, 

 though at least 230 pounds had been added to it and it contained 

 three pounds at first. 



It would seem, then, from this and other experiments, that farm 

 manure would better be spread in layers, in the barn-yard, a few 

 inches thick, till it is somewhat decomposed, and then spread thinly 

 over the fields and not plowed in deeply, unless the surface can be 

 frequently cultivated, so the air can have free access to every portion 

 of the soil containing the fertilizer. In this way the air-hating 

 bacteria will be deterred from working in the fertilizer overmuch. 



3. The work of the air-loving, nitrifying bacteria beautifully 

 complements that of the denitrifying bacteria, if they are given a 

 fair chance. As their name implies, they work best in loose soil 

 near the surface of the ground, and are nearly absent from soil at 

 a greater depth than two feet. They are of several kinds, and are 

 very numerous in rich, porous humus. Some change ammonia to 

 nitrites, and others change nitrites to nitrates. They do not work 



