THE UTILIZATION OF ENERGY. 469 
added to a materially heavier basal ration containing considerable 
grain and therefore already tolerably rich in starch and other carbo- 
hydrates. In spite of the smaller average amounts of starch added, 
then, Kellner’s results in a sense represent the percentage utiliza- 
tion of larger quantities of starch than do Ktihn’s; that is, they 
represent the utilization of starch at a greater distance above the 
maintenance ration. The average utilization (pp. 461-2) was— 
Kihn’s experiments. .................. 50.0 per cent. 
Kellner’s experiments, moderate rations... 58.4 “ “ 
. . heavy rations...... 61.5 “ « 
It would appear, then, from these figures that the metaboliz- 
able energy of starch was more fully utilized in rations containing a 
relatively large quantity of it. At least a partial explanation of 
this seems to be afforded by the variations in the production of 
hydrocarbons (methane). As was mentioned in discussing the 
metabolizable energy of starch, the conditions in Kthn’s experi- 
ments were such as to permit a considerable proportion of the 
starch to undergo the methane fermentation, while the more abun- 
dant supply of it in Kellner’s experiments resulted in reducing, or 
in some cases wholly suppressing. this fermentation of the starch. 
The effect of this, as there pointed out, was to make the metaboliz- 
able energy per gram greater in Kellner’s than in Kiihn’s experi- 
ments, but it has also another result. As we have seen, the methane 
fermentation constitutes part of the work of digestion, in the general 
sense in which that term is here employed, the amount of the latter 
being measured by the heat evolved. This amount being less in 
Kellner’s than in Kihn’s experiments, the net availability of the 
metabolizable energy of the starch should be greater, and, other 
things being equal, the storage of energy (gain of tissue) should also 
be greater. 
Kellner * computes that for each 100 grams of starch digested 
there was produced, on the average, methane corresponding to the 
following amounts of carbon: 
In Kiithn’s experiments..............-4-- 3.0 grams 
In Kellner’s experiments. .............. 23S 
* Loc. cit., p. 423. 
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