CONSTITUENTS OF PLAX'i- 



375 



pentosans are accompanied with a substance 1 which yields a fur- 

 fural-like product, but which product decomposes on standing 

 and does not distil with the furfural a second time. Pentosans 

 occur in most plant materials, and are particularly abundant in 

 hays and straws. The pentosans are chiefly gums, pectins, and 

 hemicelluloses, though a certain quantity is always found in the 

 crude fiber. 



Digested pentosans appear to be of considerable value to the 

 animal. Although it is possible that they have the same value 

 as starch, when once digested, yet the digested portion of feed- 

 ing stuffs rich in pentosans has a decidedly lower value for pro- 

 ductive purposes than that of starchy materials. This appears 

 to be due in part to the labor of chewing the crude fiber of such 

 materials, but the labor of chewing does not account for the 

 entire deficit. 



The following table shows the relative occurrence of these 

 classes of substances in different materials. 2 



NITROGEN-FREE EXTRACT OF SOME FEEDING STUFFS. 



Crude Fiber. 3 The organic residue left after extraction of 

 plant substance with ether and boiling it successively with i% 

 per cent, acid and alkali, is termed crude fiber. The process is 

 arbitrary, and the object in view when it was devised was to se- 

 cure a product as free as possible from nitrogen. 



1 N. C. Bulletin, No. 178. 



2 Fraps, Jour. Am. Chem. Soc., 1900, p. 543. 



3 See Tollens, Exp. Sta. Record 8, p. 649. 



