Pathogenesis 585 



resemble those of the cholera spirillum, being deeply situated in conical depres- 

 sions in the gelatin. Under the microscope the contents of the colonies, which 

 appear of a brownish color, are observed to be in rapid motion. The edges of the 

 bacterial mass are fringed with radiating organisms. 



Gelatin Punctures. In gelatin tubes the growth closely resembles that of the 

 cholera organism, but develops more slowly. 



Agar-agar. Upon the surface of agar-agar a yellowish-brown growth develops 

 along the whole line of inoculation. 



Potato. On potato at the room temperature no growth occurs, but at the 

 temperature of the incubator a luxuriant yellowish-brown growth takes place. 

 Sometimes the color is quite dark, and chocolate-colored potato cultures are not 

 uncommon. 



Bouillon. In bouillon the growth which occurs at the temperature of the incu- 

 bator is quite characteristic, and very different from that of the cholera spirillum. 

 The entire medium becomes clouded, of a grayish-white color, and opaque. A 

 folded and wrinkled pellicle forms upon the surface. 



Milk. When grown in litmus milk, the original blue color is changed to pink in 

 a day, and at the end of another day the color is all destroyed and the milk coagu- 



^P^ 



Fig. 245. Spirillum metchnikovi, from an agar-agar culture. X 1000 (Itzerott 



and Niemann). 



lated. Ultimately the clots of casein sediment in irregular masses, from the 

 clear, colorless whey. 



Vital Resistance. The organism, like the cholera vibrio, is very susceptible to 

 the influence of acids, high temperatures, and drying. The thermal death-point 

 is 5oC., continued for five minutes. 



Metabolic Products. The addition of sulphuric acid to a culture grown in a 

 medium rich in peptone produces the same rose color observed in cholera cultures 

 and shows the presence of indol. When glucose is added to the bouillon no fer- 

 mentation or gas-production results. The organism produces acids and curdling 

 enzymes. 



Pathogenesis. The organism is pathogenic for animals, but not for man. 

 Pf eiffer has shown that chickens and guinea-pigs are highly susceptible, and when 

 inoculated under the skin usually die. The virulent organism is invariably fatal 

 for pigeons. W. Rindfleisch has pointed out that this constant fatality for 

 pigeons is a valuable criterion for the differentiation of this spirillum from that 

 of cholera, as the subcutaneous injection of the most virulent cholera cultures is 

 never fatal to pigeons, the birds only dying when the injections are made into the 

 muscles in such a manner that the muscular tissue is injured and becomes a locus 

 minoris resistentia. When guinea-pigs are treated by Koch's method of 

 narcotization and cholera infection, the temperature of the animal rises for a 

 short time, then abruptly falls to 33C. or less. Death follows in from twenty to 



