184 BACTERIA 



present. This is the "cholera red ".reaction. If the color does not 

 at once appear, nitrites must be added. 



Pathogenesis. Cholera spirilla are pathogenic for man and 

 guinea pigs. 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 suscep- 

 tible. 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 organ- 

 ism is intra-cellular (an endo-toxin). Old cultures become patho- 

 genic through a bacteriolytic action, by which the cells are dis- 

 solved, and the toxin liberated. Filtrates from young cultures are 

 non-toxic. If bouillon cultures are killed by chloroform, and then 

 injected into animals, toxic action follows. In cholera the patho- 

 genic process is mostly confined to the intestines. Toxic absorp- 

 tions, due to the liberation of toxic products by the bacteriolytic 

 action of serum, follow later. There is a desquamation of the 

 epithelium of the bowel, and epithelial cells found in the watery 

 discharges resemble rice grains. Peyer's patches may become 

 slightly swollen and reddened, and later, there may be a diphtheritic 

 necrosis above the iliocecal valve, and often a parenchymatous 

 nephritis. The vibrios do not enter the blood. 



Diagnosis. Bacteriological diagnosis of cholera is accomplished 

 by examining the alvine discharges. A mucous flake is mixed with 

 some peptone solution, this is incubated, and the spirilla, if present, 

 rapidly grow on the surface; after a few hours, plates are poured 

 from this surface growth, and from the plates liquefying colonies 

 are picked out, and bouillon cultures made. These are tested 

 by dried serum, from horses artificially immunized by injecting 

 cholera spirilla into them. If the organism under examination 

 (after serum mixed with 2,000 to 3,000 parts of water is added) 

 agglutinates, it is considered to be the cholera spirillum. Both in 



