266 TEXT-BOOK OF BACTERIOLOGY. 



to show in cholera cultures a definite body of basic character, the 

 cadaverin or pentamethylendiamin, and pointed out the possibility 

 of its being related to certain symptoms frequently manifested in the 

 progress of the disease itself. He and Nencki have subsequently 

 found two or three other bases, proving them likewise to be poison- 

 ous by experiments in animals and suggesting the power of trans- 

 mutation of the cholera bacteria. 



"We must mention here an observation almost simultaneously 

 made by Bujwid and Dunham which shows that the cholera bac- 

 teria are the original exciters of quite important and specific chem- 

 ical processes. By treating comma-bacilli cultures grown in bouil- 

 lon containing peptone (or in common nourishing gelatin) with a 

 small quantity of sulphuric acid, there will shortly appear in the 

 solution a reddish-violet (frequently purplish-red) decoloration. 

 This is met with in the same or a similar manner only in the vibrio 

 Metschnikoff, and is absent especially in Finkler's, Emmerich's, and 

 other intestinal bacteria usually cited together with the cholera 

 bacilli. Bouillon cultures exhibit the reaction very distinctly after 

 remaining from ten to twelve hours in the incubator, while the 

 gelatin cultures furnish it only after some days, whenever liquefac- 

 tion has attacked the greater part of the culture medium. 



This specific cholera reaction is, according to Salkowski's inves- 

 tigations, nothing else but the common indol-reaction caused by 

 adding indol to nitrous acid. The cholera vibrios likewise form 

 indol from the albuminates in their cultures, for which reason 

 an addition of peptone to the medium is requisite. We might, there- 

 fore, feel inclined to find in this circumstance something peculiar 

 to them; but it can easily be proved that many other micro- 

 organisms produce indol as well. In order to produce the red color 

 reaction, it sufllces to mix their cultures with impure nitric or 

 muriatic acid containing nitrites. The point distinguishing the 

 cholera bacteria is rather their production of the nitrous combina- 

 tions which are necessary for the reaction. These arise (as shown 

 or, at least, rendered very probable by Petri) by reduction of the 

 nitrates traces of which are present in salt and peptone, and espe- 

 cially contained in the crude gelatin. "We will now readily under- 

 stand (after these explanations) that available and really decisive 

 results can be looked for only when using perfectly pure sulphuric 

 acid free from nitrites. 



The significance of the cholera reaction is very great, especially 

 for practical purposes, as it affords us a quick and sure means of 

 distinguishing the cholera bacteria from other micro-organisms. 

 Having, for instance, received material suggestive of cholera, we 



