NON-PATHOGEXIC BACILLI. 627 



attain a diameter of one to two millimetres ; they are finely granular, have a 

 dirty- white color and circular, smooth outline ; the gelatin around them ac 

 quires a steely grayish-blue shimmer. Under a low power the deep colonies 

 are seen as round discs with a dark centre and a brownish, granular mar- 

 ginal zone with a sharply defined dark contour ; the superficial colonies have 

 a dark-brown centre surrounded by a grayish-brown, and outside of this a 

 narrow, yellowish, finely granular marginal zone 

 with a sharply denned contour. In gelatin stick t , v 

 cultures a white mass develops around the point -^ f /^L \L ) '^ />\ ! *// 

 of puncture, and around it the gelatin acquires a ^ wr /}, 

 dark steel-blue color. Upon agar a grayish layer 

 is developed and the culture medium acquires a 



dark-brown color near the surface. Upon potato FIG. 210. Bacillus cyano- 

 a slimy, yellowish layer is developed, limited to genus; at a the rods contain 

 the vicinity of the impf strich ; around this the po- spores, x TOO. (Flugge.) 

 tato acquires a diffused grayish-blue color. Upon 



blood serum development occurs without the formation of pigment. In 

 milk a slightly alkaline reaction is produced by the growth of this bacillus ; 

 the casein is not coagulated ; at the surface and gradually extending down- 

 ward a slate-blue color is developed, and upon the addition of an acid this 

 changes to an intense blue. In milk which has not been sterilized and which 

 contains acid-forming 1 bacteria a sky-blue color is produced without the ad- 

 dition of an acid. The pigment is produced most abundantly at a tempera- 

 ture of 15 to 18 C. ; at 25" G. it is less abundant, and at 37 C. is not formed 

 at all. 



Note. Jordan gives an account of Bacillus cyanogenus which differs 

 materially from that above given by Fliigge, and which leads to the belief 

 that two or more different bacilli have been described under this name. 

 Jordan's description agrees tolerably well, however, with that of Heim. The 

 bacillus described by him was quite frequently found in Lawrence sewers 

 and is described as follows : 



"Morphology. Small bacilli with rounded ends, often oval in form. 

 Occur in chains in all media, isolated individuals being quite the exception. 

 The chain is usually long and its members cohere quite firmly. On no me- 

 dium has there been observed anything resembling spore formation. The 

 individuals are about 1.3 /* long and 0.8 ju broad. Motility : There is a slight 

 independent movement to be observed in hanging drops. We have certainly 

 ncD found this species to be ' very motile.' Temperature: Does not grow as 

 well at 37 as at 21 C. Need of oxygen : Grows very scantily under the 

 mica plate. Plate cultures : The young colonies below the surface of the 

 gelatin are usually slightly oval, with a coarsely granular interior and an 

 even, regular edge. Often, however, the colonies have a frayed, irregular 

 appearance to the naked eye, and with the microscope show fine branchings 

 from the centre. On coming to surface the colonies always spread out into 

 a dull, dry expansion with irregularly hacked edges. Sometimes the colo- 

 nies are surrounded by a light blue-green haze, which soon changes to a 

 faint brown ; and this becomes deeper and deeper till the whole plate is 

 colored an intense dark -brown. More often, however, in our experience, the 

 brown color comes without a previous development of the blue. In slightly 

 acid gelatin the blue color comes more surely and constantly than in the 

 ordinary alkaline medium. The gelatin is not liquefied. Tubes gelatin : 

 In about three days there is a thin surface growth, smooth and faintly lus- 

 trous. The contour is at first quite regular, with the edges only slightly 

 toothed. There is only a slight growth along the inoculation line. The 

 gelatin near the surface soon takes on a brown tint, and eventually the whole 

 tube of gelatin is colored dark-brown. The blue coloration is not observed 

 as well in tubes as on plates. This species grows fairly well in acid gelatin, 

 but not so well as in alkaline. In the former the brown color invariably comes 

 more slowly. Tubes agar : In. three days there is a good surface growth, 

 white and lustrous. The agar is colored dark-brown. The growth itself 



