INFECTIONS OF THE DIGESTIVE TRACT 187 



bacilli or atypical colon bacilli or dysentery bacilli 

 appears to have prepared the way for such a secondary 

 infection. In the case of the dysentery bacilli it is 

 probable that they have the ability to make "aggres- 

 sins" which inhibit the local or even the general defenses 

 so as to permit the free multiplication of pathogenic 

 streptococci. A similar relationship is seen in some 

 instances of smallpox, scarlet fever, and measles. It 

 seems clear that in many of these cases, in which the role 

 of the streptococci is that of a secondary invader, this 

 infection is responsible for severe exacerbations or death. 

 In adults the intestinal tract is not rarely the seat of 

 invasion by strep tococcal microorganisms. Where these 

 are virulent, they are apt to be associated with diar- 

 rhceal disorders. There are, however, instances in which 

 the streptococci are only slightly pathogenic for animals, 

 such as guinea-pigs, but are present throughout con- 

 siderable periods of time in excessive numbers in the 

 stools. Their presence may be demonstrated in the 

 Gram-stained microscopical fields, where they are seen 

 as short chains or as diplococci. In such cases these 

 organisms will be found to be abundantly represented 

 in sugar-bouillon fermentation tubes which have been in- 

 oculated from the mixed faecal flora. We have observed 

 instances in which these Gram-positive streptococcal 

 forms enormously preponderate in the sedimentary 

 fields from the fermentation tubes. It has some- 

 times happened, also, that even though the Gram-posi- 

 tive fields fail to show the streptococcal forms in such 

 abundance as to attract attention, they outgrow other 



