INFECTIONS OF THE DIGESTIVE TRACT 127 



marked examples of saccharo-butyric putrefaction the 

 quantity of gas produced may be one-half, one-third, 

 one-quarter, or even one-fifth of the normal gas produc- 

 tion. I am disposed to attribute this mainly or wholly 

 to an elimination of the colon bacilli. The gas produc- 

 tion in the sugar-bouillon tubes has in several instances 

 been observed to correspond fairly closely to the volume 

 of gas produced by the colon bacilli from the same case. 

 It is known that different strains of colon bacilli liberate 

 different quantities of gas on the same sugar-bouillon 

 medium, and I am therefore disposed to attribute 

 the fluctuations observed in health mainly to the different 

 gas-producing character of organisms of the colon bacillus 

 group. It is possible that B. lactis aerogenes plays a 

 part, but I believe this organism to have a subordinate 

 role. There are cases in which the intestine contains 

 yeast organisms, and under these circumstances there 

 is a very much larger gas production than is ordinarily 

 the case. A very abundant gas production in the sugar- 

 bouillon tubes inoculated from the faecal flora should 

 excite suspicion of the presence of yeasts. Sometimes, 

 however, the excessive gas production is dependent on 

 the growth of B. lactis aerogenes. As I have already 

 stated, this organism in pure culture does not ordinarily 

 grow in the closed limb of the fermentation tube, and 

 in order to enable it to grow it has to be aided by the 

 presence of blood or bits of sterile tissue. We have 

 observed instances, however, in which B. aerogenes cap- 

 sulatus has grown in the closed limb of the fermentation 

 tube without the addition of tissue, and I attribute this 



