1888.] New Micro-organisms from Water and Soil. 415 



The chemical action which the several micro-organisms described 

 exert upon certain solutions containing salts of ammonia and of nitric 

 acid respectively has been investigated by one of the authors, with 

 the result that whilst none of the forms in question were found to 

 oxidise ammonia either to nitrous or nitric acids, several of them 

 were found to exert a powerfully reducing action on nitrates, con- 

 verting the latter into nitrites, others were without any action on the 

 nitric acid, and others again caused the disappearance of an 

 appreciable proportion of the nitric acid without production of a 

 corresponding amount of nitrite. The authors point out that these 

 differences in the behaviour of micro-organisms when introduced into 

 solutions containing nitrates are capable of furnishing very important 

 data for distinguishing between forms which otherwise present very 

 close resemblance. Thus Bacillus subtilis and Bacillus cereus, pre- 

 viously described by them as closely resembling each other, can be 

 easily distinguished by the behaviour which they respectively exhibit 

 towards the nitrate-solution, for whilst both grow luxuriantly in this 

 medium, the Bacillus subtilis has no action on the nitric acid which 

 can be quantitatively recovered, the Bacillus cereus, on the other 

 hand, powerfully reduces the nitrate with formation of nitrite. 



The nitrate-solution employed for the purpose of these experiments 

 contained potassium phosphate, magnesium sulphate, calcium chloride, 

 calcium nitrate, invert sugar, peptone, and an excess of calcium car- 

 bonate. 



The following is a brief account of the descriptions given of the 

 various micro-organisms : — ■ 



Bacillus arbor escens. —This is seen under a high power ( x 1000 

 diameters) to be a slender bacillus giving rise to wavy threads, 

 sometimes of considerable length. No spores were observed. In 

 drop cultivations it is seen to be vibratory. 



On gelatine plates it produces highly characteristic colonies. Under 

 a low power ( x 100 diameters) the centre is seen to consist of a thin 

 axial stem with root-like branches from each of its two extremities, 

 this stem thickens as growth proceeds, and the ramified extremities 

 become so largely developed that the whole colony has the appearance 

 of a wheat sheaf. The plate is slowly liquefied, and the periphery of: 

 the colony extends irregularly and to some distance from the centre, 

 over the surface of the gelatine, giving rise to beautiful iridescent 

 colours. 



On potatoes it produces a fine deep-coloured orange pigment. 



On nitrates it has no action in the solution employed. 



Bacillus aquatilis. — This is a slender bacillus also giving rise to 

 wavy threads. No spores were observed, and the individual bacilli 

 are seen in drop cultivations to exhibit only an oscillatory motion. 



On gelatine plates the contour of the colony becomes more and 



