130 INFECTIONS OF THE DIGESTIVE TRACT 



an iron or cadmium salt leads to the reabsorption of 

 the sulphur compound, giving rise to sulphides of the 

 metals. 



In some cases fermentation tubes containing bouillon 

 (or sugar bouillon) have had added to them calcium or 

 magnesium carbonate. By maintaining the neutrality 

 of the culture medium the carbonates have influenced 

 the character of the dominant organisms in the fermen- 

 tation tubes and have thus modified the proportions of 

 the products formed and even to some extent their 

 character. 



It has been found useful to examine regularly the 

 sediments of the fermentation tubes which have been 

 inoculated with the mixed fa?cal flora. This has been 

 done as a matter of routine in a large number of in- 

 stances, the examination having been made especially 

 in the case of the four sugar-bouillon tubes and the 

 peptone-bouillon tube. The appearance of the Gram- 

 stained flora gives as a rule, but not always, an indication 

 of the dominant flora in the lower part of the intestine. 

 In tubes inoculated from normal persons, Gram-negative 

 organisms corresponding in size and form to bacteria of 

 the B. coli type grow abundantly in all the tubes. As 

 a rule they constitute the dominant flora in all the sedi- 

 ments. Generally one sees mixed with them moderate 

 numbers of Gram-positive and Gram-negative diplo- 

 cocci. Moderate numbers of organisms morphologically 

 like B. aerogenes capsulatus are seen, but these forms 

 may be wholly absent. There is an aerobic, Gram- 

 positive bacillus, resembling closely in its morphology 



