CARBOHYDRATES 461 



returned to the termites, they can again transform wood. This 

 experiment, done by Cleveland, led to the further conclusion 

 that wood-ingesting Protozoa form glycogen by splitting the 

 cellulose into cellobiose and decomposing this, in turn, to glucose, 

 from which they build up glycogen. 



The statement that no cellulose-digesting ferment is known to 

 occur apparently holds for higher animals and relatively lowly 

 forms such as the insects. But in more primitive animal types, 

 it is possible that the organism itself may handle cellulose, as is 

 true of certain Protozoa and, possibly, snails, where the ferment 

 may be produced by the snail, although this is not conclusive; 

 the snail, Hke some of the ungulates, may depend upon bacteria 

 for its cellulose digestion, the bacterial colonies living in the 

 mantle of the snail. The enzyme cellulase, from snails, whether 

 produced by the snail or by symbiotic bacteria, appears to be a 

 very sensitive agent for detecting differences between types and 

 varieties of cellulose through hydrolysis. Karrer has shown this 

 to be true and concludes from it that cellulose consists of two 

 constituents which differ in their behavior toward enzymes. 



The digestion of cellulose is not limited to animals. The 

 transformation of cellulose by fungi is well known as the dry rot 

 of wood. The manner in which the germinating tube of fungi 

 spores enters the tissue of the host and the way in which pollen 

 grains penetrate the pistil of flowers on their long journey from 

 the stigma to the ovules have long been problems of interest to 

 botanists. It is possible that the spore sprout or pollen tube 

 secretes a cellulose-digesting ferment at its growing point as it 

 moves forward. 



