204 DIGESTION OF CARBOHYDRATES 



position that cellulose, especially if no other more easily 

 utilizable foods are readily available, may be drawn on as a 

 food, and that its nutritive value is to be ascribed as equiva- 

 lent to that of starch under proper circumstances. 35 



How are we to interpret the situation? Apart from the 

 fact that cellulose fermentation extracorporeally (by in- 

 oculating a suspension of cellulose in meat extract with a 

 bit of intestinal contents) proceeds only very slowly, while 

 in the animal body large amounts of cellulose disappear rela- 

 tively quickly, in its fermentation there arise products (like 

 methane, acetic and butyric acids) which either cannot be 

 handled at all or only with considerable difficulty by the 

 economy. 36 Here is an open break in our knowledge. In 

 case cellulose really has an important value as a food (al- 

 though this does not seem so thoroughly determined as to 

 make further investigation undesirable) there must be hid- 

 den back of the method of its utilization some process of 

 which we are entirely in the dark. 



Certain recent investigations by Pringsheim 37 are prob- 

 ably of importance in this connection. If the full fermenta- 

 tive power by cellulose-splitting microorganisms, which nor- 

 mally produce only methane, hydrogen, carbonic acid, lactic 

 acid and the lower fatty acids, be inhibited by means of anti- 

 septics, or (in case of thermophilic microorganisms) by re- 

 duction of temperature, one may without difficulty find in 

 the cultures in the course of a few days glucose and cel- 

 lobiose (a disaccharid). Then, too, it must be remembered 

 that lactic acid is also readily oxydized by the body and may 

 be utilized by it. 



Importance of Infusoria in Cellulose Digestion. Per- 

 haps, too, the very reasonable hypothesis suggested by 



M W. Ellenberger and A. Scheunert, Lehrb. d. vergl. Physiol. d. Haus- 

 saugetiere, p. 354, Berlin, Parey, 1910. 



86 Cf. S. Frankel, Dynamische Biochem., p. 37, et seq., 1911. 



8T H. Pringsheim (Chem. Instit., Berlin), Zeitschr. f. physiol. Chem., 78, 

 266, 1912. 



