3 o6 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. It has been pointed out by Wathelet, and also 

 by Klein, that 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. These observers point out that 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 

 great flocculi developed which float on the surface. This 

 observation we have confirmed. It is, however, to physio- 

 logical differences between the bacilli, rather than to 

 morphological, that importance is to be attached. Several 

 important points are to be studied hereon. 



i. The fermentation of sugars. Among the earlier in- 

 vestigators of this point were Chantemesse and Widal. 

 They found that the B. coli produced an acid fermentation 

 in lactose (milk sugar). The method adopted to prove 

 this was as follows. To tubes of 2 per cent lactose bouillon 

 about i gram of sterilised calcium carbonate was added in 

 each case, and the tubes were then sterilised. On inoculat- 

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

 mentation (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. 



The fermentation of lactose by the B. coli may also be demonstrated 

 by means of Petruschky's litmus -whey. The preparation of this medium, 



