m m A B 4ft 



BIOLOGICAL PROPERTIES 397 



Numerous more or less ingenious methods have been devised to illustrate the 

 fermentation properties of the colon bacillus. Thus for instance, to an agar or other 

 medium containing lactose, a substance (e.g. fluorescin) is added which is altered or 

 intensified in colour by the acids formed out of the lactose : in other cases a reagent 

 is selected for addition to the medium which is coloured in alkaline solutions but 

 colourless in acid solutions (e.g. phenol-phthalein). Ramond's method may be 

 described as an example. 



(/) Ramond's method. Take a tube of gelatin containing 4 per cent, of lactose 

 and after melting it being careful not to apply too much heat add sufficient 

 aqueous solution of acid fuchsin (Rubin 8.) to 

 impart a red-cerise colour to the gelatin, 

 then just decolourize with a saturated aqueous 

 solution of sodium carbonate 23 drops are 

 sufficient filter, sterilize at 105 C. for 5 

 minutes and pour the now colourless medium 

 into a sterile Petri dish. The typhoid bacillus 

 produces no change of colour when sown on 

 this medium, while on the other hand the 

 colon bacillus, in virtue of the acids formed 

 from the lactose which neutralize the sodium ffi w he n grown on Ramond's agar. (After 

 carbonate, regenerates the red tint so that a Gauthie\) 

 characteristic rose - coloured area develops 



around colonies of this organism. This method is not so delicate as that with 

 litmus- tinted media. 



2. Action on neutral red. Neutral red in culture media is reduced and 

 decolourized by the colon bacillus. The typhoid bacillus has no action on 

 the dye. 



Liquefy a tube containing 10 c.c. of ordinary agar (or glucose-agar), add 3 or 4 

 drops of a sterile saturated aqueous solution of neutral red, and when the medium 

 has cooled and set sow it with the colon bacillus in stab culture and incubate at 

 37 C. for 24 hours. The medium will now no longer be red but will exhibit a 

 greenish fluorescence, and on further incubation this will soon change to a canary 

 yellow colour. This reaction has been adapted by Savage to the detection of the 

 colon bacillus in water (p. 411). 



3. Indol formation. An important and very constant characteristic of the 

 colon bacillus is the formation of indol in culture media. 



The value of the indol reaction in the diagnosis of the colon bacillus has been 

 called in question by some authors on the ground that they not infrequently fail to 

 find any indol in cultures of this organism : and Remy has shown that when the 

 colon bacillus is grown with the typhoid bacillus the former may lose its capacity 

 to produce indol. 



Recent work demonstrates that the negative results obtained by the earlier 

 observers were due to the imperfections of their technique. " The property of 

 producing indol is far less variable than is generally believed," and the indol reaction 

 furnishes one of the best tests there is for identifying the organism, provided that 

 the following precautions be observed, viz. : 



1. That peptone water and not ordinary broth be used as the culture medium. 



2. That the culture be examined between the third and the eighth day but never 

 later. 



3. That the test be performed exactly as described at p. 374. 



4. Cultures on synthetic media. The colon bacillus as a rule grows 

 luxuriantly in the different liquid media of Nsegeli, Maasse, Frankel, Remy 

 and Sugg '(p. 375). 



5. Growth on vaccinated media. If the colon bacillus be sown on a tube 

 of agar or gelatin on which the typhoid bacillus has already been grown and 

 scraped off as described above, some amount of growth generally takes place 

 which though distinct is less abundant than on tubes of new media. 



6. Growth on coloured media. The colon bacillus decolourizes both 



