122 CLINICAL BACTERIOLOGY. 



a dense center, and are surrounded by a thin, serrated, leaf- 

 like, bluish, iridescent coating, which, with high powers of 

 the microscope, exhibits a delicate linear network-arrange- 

 ment ; or they present a sharp boundary, and appear as 

 porcelain-white points half the size of a pinhead. In 

 gelatin stab-cultures a chain of small, white, spherical col- 

 onies forms along the line of inoculation, while upon the 

 surface in individual cases a roset appears, and in other in- 

 stances a hemisphere. The gelatin is never liquefied, but 

 soon exhibits a dense turbidity and distinct iridescence. In 

 all gelatin-cultures ammonia and crystals of ammonio- 

 magnesium phosphate (coffin-lid shape) are formed. In 

 agar streak-cultures a dense yellowish deposit forms, and 

 upon potatoes a brownish membrane. Bouillon is ren- 

 dered turbid, and in the case of the actively motile varieties 

 a coating is often formed. Distinct gas-formation takes 

 place in growths upon all of the nutrient media mentioned. 

 It is favored by the presence of reducing substances, and 

 by anaerobic growth. Addition of potassium nitrite and 

 sulphuric acid to peptone-bouillon cultures (i cu. cm. of a 

 0.02 per cent, potassium-nitrite solution and several drops 

 of sulphuric acid to 10 cu. cm. of bouillon) causes the de- 

 velopment of a red tint (nitroso-indol reaction). Coagula- 

 tion takes place in milk. Grape-sugar, cane-sugar, and 

 glycerin undergo fermentation. Acid urine is not altered 

 by the growth of the bacterium coli, while alkaline urine at 

 times undergoes ammoniacal decomposition. The bacterium 

 coli commune retains its vitality for a long time. 



Bacillus Aerogenes. This organism is closely related 

 to the preceding. It appears as short, nonmotile rods, 

 forming filaments, sometimes with capsules, and with- 

 out spores. They do not stain by Gram's method. Upon 

 gelatin-plates they form round, porcelain-white, prom- 

 inent colonies. In gelatin stab-cultures they form a nail- 

 like growth, and gas-formation takes place. In agar 

 streak-cultures a white, slimy deposit forms. Upon potato 

 a yellowish deposit takes place. Bouillon is rendered 

 turbid and a coating forms. Milk is coagulated. Growth 

 takes place in urine without decomposition of urea. In 

 all nutrient media energetic gas-formation takes place, and 

 in those that contain sugar acetic and formic acids are gen- 

 erated. The bacillus aerogenes is probably identical with 

 the organism described by the Guyon school as bacillus 



