Value of the Nutrients 173 



hydrates also give rise to gases which pass off nncon- 

 sumecl, though perhaps not to the same extent as is 

 the case with crude fiber, and several observers de- 

 clare that digested crude fiber is no less nutritively 

 efficient in a maintenance ration than the more soluble 

 compounds of the nitrogen -free extract. 



The question has been raised as to whether the 

 gums (pentosans) which exist so abundantly in many 

 coarse foods and in some grain products, like wheat 

 bran, are not inferior to the other more soluble carbo- 

 hydrates. It has been observed that the sugars which 

 result from the action of ferments on these bodies 

 have, in some instances, not been oxidized, but have 

 passed off in the urine as such. It appears doubtful 

 whether under normal and usual conditions this occurs 

 to any extent. The gums are constantly present in all 

 rations for farm animals, and we have no reason for 

 believing that the pentose (gum) sugars are constant 

 ingredients of their urine. 



The comparative physiological values of individual 

 albuminoids and fats we do not know very much about, 

 other than what we may judge from the determinations 

 of heats of combustion. In experimental work single 

 compounds have been but little studied. The conclu- 

 sions reached have usually been based upon the results 

 of feeding mixtures of individual albuminoids and fats 

 as they ordinarily exist in plants. 



Determinations of the heats of combustion of single 

 and mixed albuminoids and fats from various sources 

 show a variation of from 5.6 to 6 Cal. per gram for 

 the former and from 9.2 to 9.6 Cal. for the latter. The 



