BACTERIA IN THE SOIL 1 55 



food. Professor Warington, in his lectures under the Lawes 

 Agricultural Trust, has described this important germ as 

 follows : 



" The organism as found in suspension in a freshly nitrified 

 solution consists largely of nearly spherical corpuscles, varying 

 extremely in size. The largest of these corpuscles barely reaches 

 a diameter of one-thousandth of a millimetre, and some are so 

 minute as to be hardly discernible in photographs. The larger 

 ones are frequently not strictly circular, and are sometimes seen 

 in the act of dividing. 



" Besides the form just described, there is another, not uni- 

 versally present in solutions, in which the length is considerably 

 greater than its breadth. The shape varies, being occasionally 

 a regular oval, but sometimes largest at one end, and sometimes 

 with the ends truncated. The circular organisms are probably 

 the youngest. 



** This organism grows in broth, diluted milk, and other solu- 

 tions without producing turbidity. When acting on ammonia it 

 produces only nitrites. It is without action on potassium nitrite. 

 It is, in fact, the nitrous organism which, as we have previously 

 seen, may be separated from soil by successive cultivations in 

 ammonium carbonate solution." 



The elongated forms appear to be a sign of arrested 

 growth. Normally the organ is about 1.8 /^ long, or nearly 

 three times as long as the nitric organism. It possesses a 

 gelatinous capsule. '* The motile cells, stained by Loffler's 

 method, are seen to have a flagellum in the form of a spiral." 

 When grown on silica the nitrous organism appears in 

 the same two forms — zooglea and free cells — as when culti- 

 vated in a fluid. It commences to show growth in about 

 four days, and is at its maximum on about the tenth day. 

 Winogradsky found that there were considerable differ- 

 ences in the morphology of the organism according to the 

 soil from which it was taken. One of the Java soils he 

 investigated contained a nitrous organism having a spiral 



