202 DIGESTION OF CARBOHYDRATES 



Part Taken in Digestion by Enzymes Contained in the 

 Food. A number of years ago Ellenberger 26 showed that 

 enzymes contained in vegetable food itself (especially those 

 capable of reducing sugars and proteolytic enzymes) may 

 become active when the food is in course of digestion, and 

 may aid the digestive juices contributed by the animal body. 

 It was thought this was especially true of the cytases of the 

 food, 27 although apparently this has proved incorrect. The 

 fact that in autolysis of wheat seeds no diminution is mani- 

 fest in the cellulose may be taken to indicate, as Scheunert 

 believes, 28 that these vegetable cytases are of no practical 

 importance in the digestion of cellulose. 



Importance of Symbiotic Microorganisms. There is 

 nothing left, therefore, but to accept the view that the 

 digestion of cellulose is effected by the microorganisms of 

 the digestive tract. Eeference has previously been made 

 (Vol. I of this series, p. 40, Chemistry of the Tissues) to 

 the biological importance of the enormous quantities of 

 minute organisms inhabiting the intestine. "It is of the 

 greatest interest, and, in my own opinion, scarcely sufficiently 

 emphasized," says W. Biedermann, 29 "that we are here 

 dealing with a typical instance of symbiosis, in which foreign 

 microorganisms, originating from the external world, by their 

 vital processes not only facilitate and promote the thorough 

 utilization of ingested foodstuffs, but actually are more 

 capable of effecting this result than any other agents." 



Marsh-gas Fermentation. What do we actually know of 

 the mechanism of this process of utilization? In the first 

 place marsh-gas fermentation (cleared up especially by the 

 studies of Popoff, Zuntz ? Hoppe-Seyler, Tappeiner and 

 Omeliansky) should be mentioned, a process which the cellu- 



29 W. Ellenberger, Skandin. Arch. f. Physiol., 18, 306, 1906; and earlier 

 works. 



* P. Bergmann (I. Bang's Lab., Lund), Skandin. Arch. f. Physiol., 18, 

 119, 1906. 



38 A. Scheunert and W. Grimmer, Zeitschr. f. physiol. Chem., 48, 27, 1906. 



29 W. Biedermann, Handb. d. vergl. Physiol., 2' 1330, 1911. 



