INFECTIONS OF THE DIGESTIVE TRACT 103 



of patients who have lately had typhoid fever. 

 Here the explanation of the absence of symptoms is 

 doubtless to be sought in local or local and general con- 

 ditions of immunity. There appear, however, to be 

 instances in which there is no evidence that typhoid 

 fever has occurred but in which nevertheless moderate 

 numbers of organisms may be obtained from the fseces. 

 The same facts hold true for the bacilli of dysentery. 

 Duval has shown that dysentery bacilli are present 

 occasionally in small numbers in the stools of normal 

 individuals, and this observation has been confirmed by 

 others. 1 We have noted the presence of B. pyocyaneus 

 occasionally in the digestive tract of persons apparently 

 in the best of health. It is likely, however, that in all 

 these cases the pathogenic organisms in question are 

 held in check by the bacteria present in the digestive 

 tract or by the bacteria and the intestinal secretions so 

 that they are unable to multiply in a significant manner 

 or to gain entry into the cells of the mucous membrane. 

 It seems not unreasonable to suppose that errors in diet 

 or depressed general conditions favor the multiplication 

 and penetration of pathogenic bacteria that have for 

 some time been present in a slumbering state. Irritant 

 foods may possibly so alter the secretions of the digestive 

 tract as to favor definite infection by the semi-parasitic 

 bacteria that are present. 

 The considerations just mentioned as applying to the 



1 In some of the apparently normal children from whom Dr. 

 Wollstein obtained dysentery bacilli there were subsequently 

 developed the clinical indications of dysentery. 



