326 TYPHOID FEVER 



potatoes is the most important. As lias been pointed out by 

 Wathelet, and also by Klein, differences exist in the growth of 

 the two bacilli in melted gelatin. A gelatin 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 gelatin, 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 morphological, that importance is to be attached. In 

 detailing the following reactions we must note that all that can 

 be said is that under certain conditions certain effects are obtained. 

 We cannot profess to know the principles which underlie the 

 occurrence of these effects, and it may be that in several 

 apparently diverse reactions the same biological processes are 

 really at work. 



(1) The Fermentation of Sugars. Of these one of the most 

 important is the effect on lactose as first pointed out by 

 Chantemesse and Widal. This is usually demonstrated by 

 using a 1 per cent solution of the sugar in peptone-salt solution 

 placed in Durham's tubes (p. 76). If such a medium be 

 coloured with litmus the production of acid and gas by the 

 b. coli can easily be demonstrated. Similar changes caused by 

 this organism can also be observed in litmus milk and in 

 Petruschky's litmus whey. 



Chantemesse and Widal first showed that the b. typhosus 

 does not act on lactose in bouillon though decolorisation of the 

 litmus may occur. It may be stated that under most conditions 

 of making the test an acid reaction does not result and there is 

 never any formation of gas. This organism is said, however, to 

 break up lactose in litmus milk and in litmus whey with some 

 acid formation. Much would thus seem to depend upon what 

 other constituents are present in the medium, and also, it may be 

 said, on its initial reaction. 



The lactose fermenting power of the b. coli is of the greatest 

 importance ; and if MacConkey's bile-salt lactose fluid medium be 

 used, this organism and its congeners can be distinguished from 

 the b. typhosus, b. para typhosus, and from the dysentery bacilli 

 (v. infra), none of whose colonies are crimson on this medium. 



The effects of the b. coli and the b. typhosus on other sugars 

 is also of great importance. As media to which the sugars may 

 be added, either peptone-salt solution or MacConkey's bile-salt 

 media are used (q.v.). To sum up the general results it may be 

 said that b. coli produces acid and gas in bile-salt glucose, 



