THE NITROUS ORGANISM 127 



inorganic food. Professor Warington, in his lectures under the Lawes 

 Agricultural Trust, has described this organism as follows : — 



" The organism as found in suspension in a freshly nitrified solu- 

 tion 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 universally 

 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 solutions 

 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 organism 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 jelly the nitrous 

 organism appears in the same two forms — zooglea and free cells — as 

 when cultivated in a fluid. It commences to show growth in about 

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

 gypsum, to which 1 per cent, of magnesium carbonate has been added, 

 the organism grows in the same form of small brown colonies, but 

 more rapidly. Winogradsky found that there were considerable 

 differences in the morphology of the organism according to the soil 

 from which it was taken. The solution used by him consisted of 

 water containing 1 per 1000 ammonium sulphate, 1 per 1000 potas- 

 sium phosphate, and 1 per 100 magnesium carbonate. 



As we have already seen, an astonishing property of this organism 

 is its abiUty to grow and perform its specific function in solutions 

 absolutely devoid of organic matter (Munro). Some authorities hold 

 that it acquires its necessary carbon from carbonic acid. The mode 

 of culturing it was as follows : — To sterilised flat-bottomed flasks add 

 100 c.c. of a solution made of two grams of ammonium sulphate, one 

 gram of potassium phosphate, and 1000 c.c. of distilled water. To 

 this was added half a gram of magnesium sulphate, two grams of 

 common salt, and 0'4 of a gram of ferrous sulphate. Now the flask 



* U.S.A. Dept. of Agriculture: Lectures under the Lames Agricultural Trust. 

 By Robert Warington, F.R.S., 1891, pp. 58, 59. 



