664 NON-PATHOGENIC BACILLI. 



tioii, owing to the active movements of the individual bacteria; the motion 

 may be compared to the circulation of protoplasm in a cell ; this is seen after 

 forty-eight hours of growth, but ceases, as a rule, on the third day, at which 

 time the contents are seen to be coarsely granular ; a round, deep, even de- 

 pression is formed in the gelatin, which at the end of several weeks may 

 have a diameter of a centimetre; the contour of the colonies is usually 

 smooth, but may be somewhat lobate and irregular. In gelatin stick cul- 

 tures development is slow along the upper part of the line of puncture, and 



a conical-shaped cavity is formed, at the bot- 

 tom of which a precipitate accumulates, while 

 above the conical cavity is empty owing to the 

 slowness of growth and drying-up of the liq- 

 uefied gelatin. The upper part of the cone 

 often has a somewhat ringed appearance. This 

 bacillus grows well in a slightly acid medium. 

 Upon the surface of agar development occurs 

 along the line of puncture, and a very thin, 

 translucent layer is formed upon the surface. 

 Upon potato a slow and scanty growth having 

 about the same color as the cut surface of the 

 potato. In milk a slightly acid reaction oc- 

 curs and the casein is slowly precipitated; 

 FIG. 219. Bacillus circulans, after cultivation for several months the bacil- 

 from an agar culture five days old. lus no longer caused coagulation of milk. In 

 x 1,000. (Jordan.) bouillon a cloudiness is seen at the end of three 



or four days, and a considerable slimy preci- 

 pitate is formed ; no film forms upon the surface. Nitrates are slowly re- 

 duced to nitrites by this bacillus. 



346. BACILLUS SUPERFICIALIS (Jordan). 



Found frequently in sewage at Lawrence, Mass. 



Morphology. Bacilli with round ends, about 2.2 ft long and 1 n broad ; 

 solitary or in pairs. 



Biological Characters. Anaerobic, liquefying, motile bacillus. Spore 

 formation not observed. Grows at the room temperature in the usual cul- 

 ture media better at 37 C. Upon gelatin plates colonies become visible at 

 the end of forty-eight hours; under a low power they are seen to be divided 

 by irregular lines into angular lumps, giving a cracked appearance to the 

 whole colony, which is irregularly spherical in form. Upon coming to the 

 surface the colonies spread out to form a round, finely granular disc, which 

 to the naked eye looks like a projecting, translucent drop; this slowly in- 

 creases in dimensions, and the surrounding gelatin is slowly liquefied ; after 

 some days the colony has an opaque, yellowish-brown centre and a translu- 

 cent edge. In gelatin stick cultures there is a very scanty growth along the 

 line of puncture and more abundant development upon the surface; lique- 

 faction proceeds slowly, and by the end of ten days may reach the walls of 

 the test tube. This bacillus grows well in acid gelatin. Upon the surface 

 of agar a moist, lustrous, gray, translucent layer is developed; at the end of 

 several weeks this growth is still smooth and glistening, and has a light- 

 brown tint. Does not grow upon potato. Does not cause coagulation of 

 milk, which, however, acquires a slightly acid reaction. In bouillon a dif- 

 fuse cloudiness is slowly developed, and after some time a scanty white 

 sediment is seen ; no film forms upon the surface. 



347. BACILLUS RETICULARIS (Jordan). 



Found in water at Lawrence, Mass. 



Morphology. Bacilli with slightly rounded ends, about 5 n long and 1 

 /u broad ; often united in chains of eight to ten elements. 



