666 NON-PATHOGENIC BACILLI. 



Morphology. Short oval bacilli with round ends, from 0.8 to 1.9 /* 

 long 1 and from 0.7 to 1 /* broad; frequently united in pairs. 



Biological Characters. An aerobic and facultative anaerobic, lique- 

 fying, actively motile bacillus. Spore formation not observed. Grows in- 

 the usual culture media at the room temperature better at 37 C. Upon 

 gelatin plates, at the end of one or two days, spherical, yellowish colonies 

 are seen ; upon coming to the surface these form a slight bluish expansion 

 with irregularly notched edges, and liquefaction of the gelatin quickly oc- 

 curs; under the microscope the colonies are seen to have an opaque centre 

 surrounded by a translucent zone and a darker margin ; the interior is finely 

 granular ; liquefaction of the entire plate occurs within three or four days. 

 In gelatin stick cultures development occurs along the line of puncture, and 

 liquefaction rapidly occurs; later an iridescent film is seen upon the surface 

 of the gelatin and an abundant flocculent, whitish sediment at the bottom of 

 the tube. This bacillus grows well in slightly acid gelatin. Upon the sur- 

 face of agar a moist, slimy, porcelain-white layer is developed ; an abun- 

 dant growth also occurs along the line of puncture in agar stick cultures. 

 Upon potato a prominent, yellowish-white layer is quickly formed. In 

 milk coagulation occurs in about four days, with a strongly acid reaction . 

 In bouillon a diffuse cloudiness is seen at the end of two days, and at the end 

 of ten to fourteen days an abundant whitish sediment is seen ; a slight film 

 forms upon the surface; this falls to the bottom when the tube is disturbed; 

 the bouillon is still clouded at the end of two or three weeks. This bacillus 

 reduces nitrates, in bouillon, vigorously. 



350. BACILLUS DELICATULUS (Jordan). 



Found in the water supply at Lawrence, Mass. 



Morphology. Bacilli about 2 jo. long and 1 ju. broad; often united in 

 pairs or in short chains. 



Biological Characters. An aerobic, liquefying, actively motile bacil- 

 lus. Spore formation not observed. Grows in the usual culture media at 

 the room temperature somewhat better at 37 C. Upon gelatin plates the 

 young colonies are seen as whitish, homogeneous spheres with a regular, ra- 

 diating margin ; at the end of two days liquefaction of the surrounding 

 gelatin occurs In gelatin stick cultures liquefaction progresses rapidly 

 along the line of puncture and is complete in about seven days ; a thick, 

 whitish layer is then seen upon the surface, and an abundant flocculent, 

 brownish deposit at the bottom of the tube ; the liquefied gelatin remains 

 clouded. Grows well in slightly acid gelatin. Upon the surface of agar a 

 wrinkled, grayish layer is developed, which later becomes porcelain-white 

 and glistening ; development also occurs along the line of puncture in agar 

 stick cultures. Upon potato a thin, spreading, gray layer is developed. 

 Milk acquires a strongly acid reaction and is coagulated. Bouillon quickly 

 becomes clouded ; a white film forms upon the surface and a white deposit 

 is seen at the bottom of the tube. Nitrates are quickly and completely re- 

 duced to nitrites by this bacillus. Does not grow at a temperature below 

 15 C. , and quickly dies out in artificial culture media in a few weeks. 



351. BACILLUS AQUATILIS (Frankland). 



Found in water often almost the only microorganism in water from a 

 deep well in the chalk formation at Kent. 



Morphology. Bacilli about 2. 5 y in length; grow out into filaments of 

 17 /* or more in length resembles Bacillus arborescens (Frankland). 



Biological Characters. An aerobic, liquefying, motile bacillus. Ex- 

 hibits oscillatory movements only. Spore formation not observed. Grows 

 very slowly in the usual culture media at the room temperature. Upon 

 gelatin plates the deep colonies are at first smooth in outline, later the mar- 



