66 INFECTIONS OF THE DIGESTIVE TRACT 



which might be brought forward, plainly point to the 

 presence of acetic acid fermentation as a normal process 

 in many healthy animals. If the material employed be 

 distilled after the addition of alkali instead of acid, one 

 obtains the volatile alkali; namely, ammonia. The 

 quantity of ammonia found is moderate and about suf- 

 fices to neutralize the acetic acid which is present. 



Action of the Mixed Fcecal Flora upon Various Media. 

 - As already mentioned in describing the action of the 

 mixed faecal flora from the nursling, the products of 

 bacterial action are determined in important ways by 

 the nature of the medium, and both their quality and 

 quantity are influenced in important ways by the readi- 

 ness with which bacteria grow upon the various media. 

 If we grow the mixed flora from a normal bottle-fed child 

 upon sugar bouillon, there is always a production of gas 

 hi the fermentation tube, and this production of gas is 

 usually greatest in lactose bouillon. A less production of 

 gas is seen in dextrose and levulose and the slightest is 

 observed in saccharose. By making strongly alkaline 

 with sodium hydroxide one may measure the amount of 

 carbon dioxide that has been formed, and such observa- 

 tions have shown that from one-third to two-thirds of 

 the gas produced under these circumstances is carbon 

 dioxide. The composition of the remaining gas is not 

 yet definitely known, but it consists mainly of hydrogen 

 and probably in part of methane. It will be found 

 on using litmus paper that there has been a production 

 of acid at the same time that gas was produced. 

 Acetone is not usually detectable in sugar-bouillon 



