304 



Mary Davits Swartz, 



In this experiment, the Cetraria islandica was carefully washed, 

 extracted with a dilute solution of potassium carbonate, to remove 

 the bitter principle; again thoroughly washed, dried and ground to 

 a powder. This preparation contained 72.5 per cent carbohydrate as 

 dextrose. The carbohydrates of the diet, throughout the experiment, 

 were limited to fine white bread and zwieback, forms in which they are 

 utilized in man to 98 per cent. The faeces were hydrolized with dilute 

 acid, and the carbohydrates determined as dextrose by AUihn's gravi- 

 metric method. It is evident that nearly all of the Cetraria carbo- 

 hydrate escaped digestion and was recovered in the faeces. 



Through the kindness of Professor Mendel, the protocol of a similar 

 experiment, by Mr. S. W. MacArthur, is also reproduced, in which 

 the technique was practically the same as described for Dr. Myers's 

 experiment. 



Cellulose-Free. 



COMPOSITION OF THE FAECES. 



Weight 

 Moist. 



Weight 

 Air Dried. 



Dextrose. Dextrose. 



Fore = 3 days. . . .: Meat, etc. 



Mid = 3 days . . . . : Meat + Cetraria* 



After = 3 days. . . .i Meat, etc. 



GraTns. 



281 

 542 

 284 



Grams. 



90.0 

 149.0 



87.5 



Per cent. 



4.4 



27.6 



4.9 



Grams. 



3.96 



34.5* 



4.2 



* Amount Cetraria eaten = 47 grams, which would be equivalent to 34.1 grams of dextrose 

 in faeces. 



It is evident that the results of this experiment simply confirm those 

 of Dr. Myers, and demonstrate that uncooked Cetraria, although 

 taken in a form as favorable as possible for its digestion, is scarcely 

 affected by its passage through the alimentary canal, and must be 

 classed among the indigestible carbohydrates. Very desirable expe- 

 riments on the digestibility of the peculiar carbohydrate of Cetraria — 

 lichenin — are also being conducted, which may throw new light on 

 the digestibility of the dextrans, but at present we certainly have no 

 grounds for assuming that this group of hemicelluloses deserves to be 

 classed with the true nutrients; all experiments show that they are 

 not attacked by animal enzymes, and are recovered unchanged in the 

 faeces after feeding. 



In conclusion, attention may be called to certain data from Japan- 

 ese dietary studies, given by Oshima (15), as to the digestibility of 



