102 INFECTIONS OF THE DIGESTIVE TRACT 



found that the fsecal suspensions gave on the gelatin 

 plates large numbers of bacteria of the type just men- 

 tioned and in addition contained considerable numbers 

 of true colon bacilli. One month after the first exami- 

 nation the fsecal suspensions showed the presence of 

 large numbers of colon bacilli, which had now become the 

 dominant type. From the litmus gelatin plates a very 

 small proportion of bacteria were isolated which were 

 incapable of coagulating milk, made no indol, and had 

 little effect^jifLQn the sugars. It was evident that the 

 substituted bacteria were now in a small minority. 

 The substituted microorganisms in this case resembled 

 the bacilli of typhoid fever except in the fact that they 

 were able to ferment glucose and possessed the ability 

 to ferment lactose and levulose in an irregular manner. 

 I have in several instances met with cases of substi- 

 tution in which the colon bacilli have disappeared from 

 the stools and have been replaced temporarily or per- 

 manently by other types of bacteria. Dysentry bacilli 

 may temporarily replace obligate colon bacilli. 



THE PRESENCE OF PATHOGENIC BACTERIA IN THE 

 DIGESTIVE TRACT IN HEALTH 



Evidence is gradually accumulating which goes to 

 show that pathogenic microorganisms may be present 

 in moderate or even considerable numbers in the intes- 

 tinal tract under some conditions without giving rise 

 to clinical manifestations of deranged function. It is 

 now well known that moderate numbers of typhoid 

 bacilli may in some instances be found in the stools 



