790 SUMMARY OF CURRENT RESEARCHES RELATING TO 



wcro without nny action on nitric acid ; nnd others again cauecd the dis- 

 appoarancc of an appreciable proportion of the nitric acid without the 

 production of a corresponding amount of nitrite. These differences in 

 the behaviour of micro-organisms wlien introduced into solutions con- 

 taining nitrates, are capable of furnishing important data for distinguish- 

 ing between forms which otherwise present a very close resemblance. 



Thus Bacillus suhtilis and Bacillus ccreus, which closely resemble 

 each other, can be easily distinguished by their behaviour towards the 

 nitrate solution ; for whilst both grow luxuriantly in this medium, 

 Bacillus suhtilis has no action on the nitric acid, which can be quantita- 

 tively recovered ; Bacillus cereus powerfully reduces the nitrate with 

 formation of nitrite. 



The nitrate solution employed contained potassium phosphate, 

 magnesium sulphate, calcium chloride, calcium nitrate, invert sugar, 

 jieptone, and an excess of calcium carbonate. 



The following is a brief account of the various micro-organisms : — 

 Bacillus arhorescens, under a high power ( x 1000) is a slender bacillus 

 giving rise to long wavy threads ; no spores were observed. In drop 

 cultivations it is seen to be vibratory. On gelatin plates ( X 100) the 

 centre of the colony consists of a thin axial stem, with root-like branches 

 from each of its two extremities, which, when largely developed, give 

 the whole colony the appearance of a wheat-sheaf. The plate is slowly 

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

 On nitrates it has no action in the solution employed. 



Bacillus aquatilis. — A slender bacillus giving rise to wavy threads. 

 No spores were observed. The individual bacilli in drop cultivations 

 show only an oscillatory motion. Gelatin is liquefied very slowly by 

 this bacillus, which grows with great difficulty in all the media except 

 the aqueous solution, wherein it grows abundantly. It does not convert 

 nitrate into nitrite. 



Bacillus liquidus. — A short fat bacillus of very variable dimensions. 

 In drop cultivations they are exceedingly motile and usually in pairs. 

 Gelatin is rapidly liquefied into large circular depressions with clear 

 contents. On agar is produced a clear shining expansion, and on potato 

 a thick flesh-coloured pigment. The nitrate in the aqueous solution is 

 powerfully reduced. 



Bacillus vcrmicularis. — A large bacillus with rounded ends giving rise 

 to vermiform threads. It produces fine oval spores. In drop cultivations 

 it shows oscillatory motion only. It powerfully reduces nitrates to 

 nitrites. 



Bacillus nnhilus. — A fine slender bacillus giving rise to wavy threads ; 

 no spores observed. In drop cultivations the isolated bacilli show 

 violent circular movements ; on gelatin plates only patches of cloudy 

 expansions with, in some cases, a faintly defined centre. Gelatin is 

 rapidly softened and liquefied. In the aqueous solution it reduces a 

 small proportion of nitrate to nitrite. 



Bacillus ramosus. — A large bacillus much resembling B. suhtilisy 

 giving rise to long threads and spores which are, however, rounder in 

 shape than those of the latter organism. Slight oscillatory movements 

 seen in drop cultivations. On gelatin plates the colonies show a cloudy 

 centre with tangled root-like branches which extend in every direction. 

 The gelatin is liquefied. In tulics the gelatin first becomes impregnated 

 with fluffy ramifications, later liquefaction ensues, and a tough pellicle 



