326 TYPHOID FEVER. 



The Comparative Culture Reactions of the B. typhosus 

 and the B. coli. The importance of the relationships 

 between the B. typhosus and the B. coli has caused great 

 attention to be paid to their biological characters, in order 

 to facilitate the distinction of the one from the other. 

 Some of these we have already noted. Of the morpho- 

 logical characters the growth on potatoes is the most 

 important. As has been pointed out by Wathelet, and 

 also by Klein, differences exist in the growth of the two 

 bacilli in melted gelatine. A gelatine tube is inoculated, 

 and, instead of being kept at the room temperature, is 

 placed in the incubator at 37 C., at which temperature 

 it is of course fluid. In such cultures, in the case of the 

 B. typhosus, there is a general turbidity of the gelatine, 

 while with the B. coli there are large flocculi developed 

 which float on the surface. It is, however, to physiological 

 differences between the bacilli, rather than to morphologi- 

 cal, that importance is to be attached. Several important 

 points are to be studied hereon. 



(i) The Fermentation of Sugars. Chantemesse and 

 Widal were the first to show that the B. coli produced an 

 acid fermentation in lactose (milk sugar). Their method was 

 as follows. To tubes of 2 per cent lactose bouillon about 

 i gramme of sterilised calcium carbonate was added in each 

 case, and the tubes were then sterilised. On inoculating 

 such a tube with B. coli, the acid produced by the fermen- 

 tation (chiefly lactic acid) acts on the calcium carbonate, 

 setting free bubbles of carbon dioxide which collect on the 

 surface of the liquid. The production of acid in lactose 

 gelatine by the B. coli can also be observed by adding to 

 tubes sufficient blue litmus to make the whole distinctly 

 blue. If a stab culture be made in such a tube, a red 

 colour diffuses out in the gelatine from the line of growth, 

 and bubbles of gas also form. Later the medium becomes 

 decolorised by reduction of the litmus. The addition of 

 lactose or other sugars to a simple solution of peptone, 

 however, gives more accurate results (p. 86). 



