Nutrition Investigations. 361 



fact that it contained a high percentage of starch (26 per cent). The 

 amount of undigested carbohydrate excreted in the faeces is in close 

 agreement with the quantity of pure mannan ingested. However, 

 as tests for mannose-hydrazone were negative in these cases, further 

 experiments are necessary before an authoritative statement can be 

 made in regard to this question. 



It is manifestly possible for faecal and soil bacteria to produce 

 sugar from mannan ;i hence it is not unlikely that hemicelluloses of 

 this group are inverted in the intestines through the activity of micro- 

 organisms, and that the sugar so produced is absorbed and becomes a 

 true source of energy for man, in spite of the resistance of mannans to 

 the action of digestion enzymes. Further investigations to determine 

 its exact nutritive value seem highly desirable. 



In considering the proper place in the dietary for marine algae, 

 lichens and similar substances, we must not disregard the possibility 

 of their having a valuable function entirely aside from the question 

 of energy production. As Oshima (15) points out, they may be val- 

 uable for their inorganic salts. The non-irritating, laxative proper- 

 ties of many species make them desirable adjuncts to the diet of per- 

 sons with a tendency to constipation ;2 and even if they disappear, in 

 marked degree, from the alimentary tract during the process of diges- 

 tion, they may perhaps still play an important role as stimulants to 

 intestinal activity, being in fact what Prausnitz' calls "faeces-forming 

 foods." An illustration of this effect is afforded by the experiments 

 in which salep powder was fed to dogs.^ The periods were equal in 

 length, and in one case (No. 2 in photograph) the utilization of carbo- 

 hydrates was equally good for all three; yet in the mid-period there 

 is a decided increase in the bulk and weight^ of the faeces, not more 

 than 1 gram of which is by any possibility attributable to the cellu- 

 lose of the salep powder, and in the other experiment, the increased 

 amount of faeces cannot be wholly accounted for by the amount of 

 undigested carbohydrate present. 



Mendel (196) has already sounded a warning against the hasty 

 assumption that every carbohydrate, by virtue of its ultimate chem- 

 ical composition, stands in the category of true nutrients for the human 

 organism. The results of the present investigations emphasize the 



^ Cf . Sawamura (267) . 



2 Cf. p. 283. 



'Zeitschrift fiir Biologic, v. 35, p. 335 Q897). 



^ Cf. pp. 348-349. 



s Cf. Table, p. 348, Series C, Experiments Nos. 1 and 2. 



