364 Alary Davies Swartz, 



cent notwithstanding their apparent resistance to amylolytic enzymes 

 and the hydrolyzing influence of the gastric juice; their disappear- 

 ance seems therefore directly attributable to bacterial activity, and 

 the possibility of sugar formation by this agency having been demon- 

 strated, it remains to be shown by means of respiration experiments 

 to what extent materials so hydrolyzed can serve as true nutrients for 

 the organism. Dogs can also utilize the dulse pentosan to a consider- 

 able degree, but their power to digest mannan is still an open question. 

 In striking contrast to the above hemicelluloses stand the galac- 

 tans, with their high degree of resistance to bacterial decomposition; 

 they show in man, an average digestibility of approximately 25 per 

 cent, in dogs of 45 per cent. It is manifestly impossible to treat of 

 the digestibihty of hemicelluloses as a class, in view of such diversity 

 in the groups. Not only must each type receive special considera- 

 tion, but distinction must be drawn between soluble and insoluble forms, 

 as is illustrated by the pentosans, the ratio of the digestibility coeflS- 

 cient of the former to the latter being approximately 100 to 50 in man, 

 and 75 to 25 in dogs. We may, however, say in general, that they disap- 

 pear from the alimentary tract of men and animals to an extent seem- 

 ingly proportional to their susceptibility to attacks of micro-organ- 

 isms, and give little justification for any high claims made for them as 

 sources of energy in nutrition. They may, however, have a valuable 

 function as adjuvants in the dietary, as therapeutic agents in consti- 

 pation, or as sources of inorganic salts. 



The author gratefully acknowledges the helpful suggestions and 

 criticism freely given by Professor Lafayette Mendel throughout the 

 progress of this work and the kindly interest and assistance of Pro- 

 fessor Rettger in the bacteriological problems. 



