BIOLOGICAL PROPERTIES 373 



SECTION III. BIOLOGICAL PROPERTIES. 



The difficulty of distinguishing the typhoid from the colon bacillus has 

 rendered necessary a close study of the biological properties of the two 

 organisms : the morphological characteristics alone are insufficient to allow 

 of their differentiation. 



1. Biochemical reactions. 1 



Action on carbohydrates. The typhoid bacillus has a distinct action 

 [acid without apparent gas] upon glucose, [maltose, sorbite and mannite] 

 and also acts feebly upon Isevulose and galactose, but ferments neither 

 saccharose, lactose, [dulcite, raffinose, arabinose, erythrite, salicin, amygdalin 

 nor inulinj. 



These properties furnish valuable data for the recognition of the organism, 

 and the methods of demonstrating them will now be considered. 



(a) Sow the bacillus in a tube of lactose-broth to which a little carbonate 

 of lime has been added (p. 35). No gas is formed however long the culture 

 be incubated. 



(6) Sow on litmus-lactose-gelatin (p. 57) : the typhoid bacillus does not 

 attack either mannite or lactose so that no acid is formed and the medium 

 retains its blue colour (cf. Bacillus coli). 



(c) Sow in Grimbert and Legros' medium. This medium has the following 

 composition : 



Lactose (chemically pure), 20 grams. 



Peptone, 5 ,, 



Distilled water, - 1000 c.c. 



Dissolve by boiling : add a little pure carbonate of lime : shake : leave for 

 5 minutes : filter : test the reaction, which should be neutral. Sterilize by filtering 

 through a Chamberland bougie. Distribute into tubes and add sufficient sterilized 

 litmus solution (p. 56). 



After sowing with the typhoid bacillus and incubating, the medium retains 

 its blue colour. 



(d] Sow in milk. The milk is not coagulated and if a little litmus solution 

 be added its colour remains unchanged. 



[A definite acidity is produced in the first 24 hours but this is subsequently 

 neutralized and the medium ultimately becomes distinctly alkaline, though 

 the time occupied in the production of an alkaline reaction varies considerably 

 with different strains in some cases a month may elapse before the medium 

 is definitely alkaline. ] 



For these tests the milk should always be sterilized at the same known tempera- 

 ture : some contaminating organisms which easily coagulate milk which has been 

 sterilized at 100 C. coagulate it more slowly and with more difficulty if it has been 

 exposed to higher temperatures, and mistaken diagnosis may result if this fact has 

 not been recognized (see also p. 57). 



These reactions are sufficient to enable the typhoid bacillus to be dis- 

 tinguished from the colon bacillus (p. 393). When it is necessary to make a 

 differential diagnosis between the typhoid and colon bacilli glucose should 

 never be used as the fermentable agent since the typhoid bacillus has a distinct 

 action on it. 



Non-production of indol. The typhoid bacillus never produces indol in 

 cultures. 



1 Here the nature of the reactions will be briefly stated ; their application to the 

 differentiation of the typhoid and colon bacilli will form the subject of a special chapter 

 (xxiii.). 



