172 The Feeding of Animals 



this is a doubtful assumption. The nitrogen-free ex- 

 tract digested from the fodders is much more largely 

 derived from crude fiber and the gums than that di- 

 gested from the grains, starch being predominant in 

 the latter, and we are not justified in concluding, 

 except from reliable evidence, that the materials from 

 the two sources are similar and equivalent as nutrients; 

 in fact, some investigators believe the reverse to be 

 true. 



If we accept the heat of combustion of the carbo- 

 hydrates and similar substances when burned in a cal- 

 orimeter as the measure of their energy value, we have 

 definite figures. The heats of combustion of the com- 

 pounds found in the nitrogen-free extract have been 

 found to vary from 3.7 to 4.2 Calories per gram. 

 This indicates no great difference in value for the 

 production of heat energy. We are not sure, how- 

 ever, that what is true of simple, rapid combustion is 

 true of physiological use. Certain related facts must 

 be considered. Because of Tappeiner's conclusion that 

 the fermentations to which cellulose is subject, break 

 it up mostly into gases and organic acids which he 

 regarded as largely not useful to the animal, the view 

 has more or less prevailed that digested crude fiber is 

 greatly inferior to starch as a nutrient. More recent 

 investigations throw doubt upon the correctness of 

 this view, and the trend of opinion now seems to be 

 towards regarding cellulose as taking practically the 

 same place in nutrition, apart from ease of digestion, 

 that starch does. It appears that the fermentations 

 in the digestive tract of starch, sugar and other carbo- 



