THE COMMA BACILLUS OF ASIATIC CHOLERA 155 



watery solution of peptone, to which ^ per cent, of chloride of sodium is 

 added, and if the peptone used is not alkaline, then the medium must be 

 rendered alkaline with a solution of soda. 



Specific Reactions. When a drop of pure reduced hydrochloric 

 or sulphuric acid is added to cultures of cholera bacilli grown in peptone 

 media, a rose or purple-red colour results, which is known as the 

 nitroso-indol reaction. The comma bacilli possess the faculty of first 

 forming indol, and then changing the traces of nitrates in the culture 

 solution into nitrites. Other vibrios exhibit the nitroso-indol reaction 

 besides the cholera vibrio, i.e., vibrio Mentschnikoff vibrio Berolinesis 

 (see section on Water Bacteria, page 206). Finkler and Prior's vibrio and 

 Denecker's cheese vibrio also form indol, but no nitrite, the addition of 

 a pure acid that does not contain nitrous acid producing no red colour. 

 In bouillon, under certain circumstances, the reaction fails when either 

 too much or too little nitrates are present. 



There are two methods whereby genuine cholera bacilli are 

 differentiated from other similar vibrios, known as Pfeiffer and Gruber's 

 reactions. 



(1.) Pfeiffer 's Reaction is produced as follows : Some blood serum of 

 a guinea-pig or other animal rendered immune to cholera is reduced 

 with ordinary bouillon in the proportion of 1 to 100, and in 1 c.c. of 

 the above mixture, a- platinum loop (capable of holding about 2 mg.), 

 full of the vibrio species under investigation, is added, and the inoculated 

 mixture injected into the peritoneal cavity of a guinea-pig weighing about 

 200 grams. Every five minutes some of the peritoneal effusion forming 

 is removed by means of fine glass capillary pipettes, and examined, 

 both stained and unstained. If it is the genuine Koch's comma bacillus, 

 they will be observed to become non-motile first, then transform them- 

 selves into small balls, which finally, in about twenty minutes, become 

 quite loosened. When the above phenomena are absent, then the 

 vibrio belongs to another species. To prevent an error arising, a 

 control guinea-pig is inoculated iiitraperitorieally with 1 c.c. of normal 

 serum bouillon mixture, 1 to 100, to which one loop of the suspected 

 culture is added. If in twenty minutes the peritoneal effusion contains 

 living motile bacilli (which were killed with immune serum), then the 

 diagnosis of Asiatic cholera can be given with safety. 



(2.) Gruber's Reaction. A small portion of the vibrio culture under 

 investigation is placed with the serum of an animal vaccinated against 

 cholera in the proportions of 1 to 50, 1 to 100, and upwards. The mix- 

 ture is examined at once with a high power. If the vibrio become 

 non-motile, flock together in herds, and agglutinate, then the bacilli 

 are without doubt genuine cholera vibrio. 



A macroscopic agglutination can also be procured by inoculating 

 bouillon with the suspected vibrio and adding cholera-immune serum in 



