THE UTILIZATION OF ENERGY. 471 
It may be remarked further that the rations in Kiihn’s experi- 
ments differed materially from those ordinarily used in practice, 
both as to their make-up and their very wide nutritive ratio, so 
that the conditions may fairly be regarded as in a sense abnormal. 
Kellner’s rations represent more nearly normal conditions, and 
they fail, as we have seen, to give any clear indications of an in- 
fluence of amount of food upon the proportion of energy utilized. 
Whether other feeding materials show a behavior analogous to that 
of starch, future investigations must decide. In the meantime 
we are apparently justified in discussing such results as are now 
on record upon the provisional hypothesis that, within reasonable 
limits, the utilization of energy is independent of the amount of 
food, or, in other words, is a linear function. 
Influence of Thermal Environment.— The influence of the 
thermal environment of the animal upon its heat production and 
upon the net availability of the energy of the food has already been 
fully discussed in previous pages and needs only a brief consider- 
ation here. 
RumInANtTs.—We have already found reason to think that in 
ruminants the heat production on the ordinary maintenance ration 
is in excess of the needs of the body. Kiihn’s and Kellner’s results 
show us that from 25 to 72 per cent. of the metabolizable energy 
of the food supplied in excess of the maintenance requirement was 
converted into heat, so that the heat production was frequently 
increased 40 or 50 per cent. above that which was observed on the 
maintenance ration. Under these circumstances we can hardly 
suppose that any moderate changes in the thermal environment 
would sensibly affect either the availability of the food energy or its 
percentage utilization. 
The writer is not aware of any exact determinations of the 
influence of the thermal environment upon the heat production of 
fattening ruminants, but the above conclusion is in harmony with 
the practical experience of many feeders that moderate exposure 
to cold is no disadvantage, but rather an advantage in maintaining 
the health and appetite of the’animals, and it appears also to have 
the support of not a few practical feeding trials.* 
* Compare Henry, “Feeds and Feeding,” second edition, p. 364, and 
Waters, Bulletin Mo. Bd. Agr., September, 1901, p. 23. 
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