DIGESTION AND RESORPTION 91 



129. Pentosans. The pentosans are widely distributed 

 in the vegetable kingdom and appear to be contained chiefly 

 or wholly in the cell walls of plants, probably in combination 

 to a greater or less extent with hexosans. If the ordinary 

 methods of feeding stuffs analysis are followed, both the crude 

 fiber and nitrogen-free extract contain them (109, 110). 



Stone, 1 who was the first to show that they were digestible, 

 found a percentage digestibility of about 60 for the pentosans 

 in the ordinary feed of the rabbit. Later, 2 in conjunction with 

 Jones, he showed that in 14 different samples of roughages 

 from 48 to 90 per cent of the pentosans were digested by sheep, 

 while in mixed rations the corresponding figures were from 46 

 to 71 per cent. Weiske 3 about the same time obtained similar 

 results in experiments with sheep and rabbits. The digesti- 

 bility of pentosans has been fully confirmed by later experiments. 



But while pentosans are digestible, or at least disappear in 

 the digestive tract, the manner of their digestion is not cer- 

 tainly known. Up to the present time no enzyms have been 

 discovered either in the digestive organs or elsewhere, which 

 have been proved to be capable of hydrolyzing them. On the 

 other hand, however, the pentosans are attacked by bacteria 

 much like other carbohydrates and yield similar products, 

 especially the acids of the aliphatic series. That the pentosans 

 are to a considerable extent subject to the methane fermenta- 

 tion in the digestive tract seems clear from Kellner's investi- 

 gations upon straw pulp (128) , in which over one- third of the di- 

 gested organic matter consisted of pentosans, so that it is difficult 

 to resist the conclusion that these, as well as the cellulose, under- 

 went fermentation. Moreover, in a large number of similar 

 experiments, the methane fermentation has been found in a 

 general way to be proportional to the total digestible crude 

 fiber and nitrogen-free extract, including the pentosans. Of 

 course these results do not preclude the possibility of a hy- 

 drolysis of the pentosans in the digestive tract, converting them 

 into pentose sugars, but as yet there is no direct evidence that 

 such a process takes place. If it does not, then the products of 

 the digestion of the pentosans are substantially the same as 

 those from cellulose. 



1 Amer. Chem. Jour., 14 (1892), 9. 2 Agricultural Science, 7 (1893), 6. 



3 Ztschr. Physiol. Chem., 20 (1895), 489, ' 



