82 UNIVERSITY OF WISCONSIN STUDIES 



This figure shows these 615 cultures in three distinct groups 

 based on the relation of the volume of carbon dioxide and 

 hydrogen produced. By far the larger number produced 

 carbon dioxide and hydrogen in almost equal amounts, thus 

 giving a ratio of approximately 1 :1. The average was 

 CO a /H=rl.06, with only an occasional culture giving less 

 COo than H., and comparatively few varying appreciably on 

 the other side of the mean. It was observed that as the 

 technique of the gas determinations became more refined, the 

 variation in the gas ratio became less, and it is probable that 

 the greater part of the variation shown for this group is in 

 the determinations rather than in the fermentation. The 

 volume of gas produced by this group is relatively small. 

 From 10 c. c. of 1 per cent dextrose broth about 14 c. c. of 

 gas was produced. Of the 350 cultures giving the 1.06 ratio 

 only 3 liquefied gelatin. These will be considered later with 

 the liquefying cultures. 



Distinctly separated from this group so far as the gas 

 ratio is concerned is a second type characterized by the pro- 

 duction of considerably more C0 2 than H.,, by a wider range 

 of ratio, and by a greater variation in the gas ratio of in- 

 dividual cultures. Nearly all of the liquefj'ing cultures be- 

 long in this group. A study of the tables and figures in some 

 of our previous papers will show that the actual amount of 

 hydrogen produced is nearly constant throughout these two 

 groups and that the increase in the ratio is brought about 

 almost entirely by a larger production of carbon dioxide. 



In our first paper"' we suggested, as a possible explanation 

 of the remarkable constancy of the B. coli ratio of 

 CO Z /H 2 =1.06 and the variation found in the aerogenes ratio, 

 that the equal volumes of carbon dioxide and hydrogen were 

 produced by a fermentation common to both groups while 

 in the aerogenes group there occurs an additional and in- 

 dependent fermentation producing carbon dioxide only. 



Clark has shown that while an increase of sugar in the 

 medium has no appreciable effect on the relation of C0 2 to H 2 



Loc. cit. 



