204 BACTERIA 



becomes more and more granular, and finally the whole medium 

 is liquefied. In gelatine tube stab culture, the growth, at first, is 

 not characteristic; but, after a few hours, a semi-spherical depres- 

 sion appears, which extends downward, and resembles a large 

 bubble of gas. As liquefaction progresses, the whole line of punc- 

 ture disappears, and the excavation looks cylindrical. This area 

 becomes cloudy. On agar plates the colonies are elevated, round 

 and white, with moist lustre. Deep colonies are whetstone shape. 

 Old agar colonies become yellowish-brown. Coagulated blood 

 serum is rapidly liquefied at 37C. Milk, at times, is coagulated. 

 No curdling ferment is formed; the acid produced is thought to be 

 sufficient. On potato the growth is slow, or not at all, if the 

 medium is acid. If the potato is rendered alkaline, growth occurs, 

 with a moist lustre, slightly elevated; white at first, later becoming 

 brown. On acid fruits it will not grow. In bouillon, after sixteen 

 hours, a diffuse cloudiness occurs, with the formation of a stiff 

 pellicle, which in some cultures becomes wrinkled. In peptone, 

 abundant growth takes place, with the production of indol and 

 nitrites. If a few drops of H 2 SO4 are added, a beautiful red 

 appears if nitrites are present. This is the " cholera red " reaction. 

 If the color does not at once appear, nitrites must be added. On 

 blood media certain strains produce distinct hemolysis (El Tor). 

 Pathogenesis. Cholera spirilla are pathogenic for man, but 

 only under experimental conditions, for lower animals for which 

 guinea pigs may be taken as an example. If the stomach of the 

 latter is rendered alkaline with bicarbonate of soda, and a bouillon 

 culture introduced, choleraic symptoms will follow and the animal 

 will die. If cholera spirilla are injected into the peritoneum, the 

 animal will quickly succumb to a general cholera peritonitis. 

 Young rabbits are equally susceptible. When cholera spirilla in 

 culture have been swallowed by man (laboratory workers), either 

 by design or accident, the disease has followed, sometimes with 

 fatal results. The toxin of this organism is intracellular (an 

 endo-toxin). Old cultures become pathogenic through a bac- 



