THE UTILIZATION OF CERTAIN PENTOSES 
difference between the amount remaining in the culture solutions 
and the amount recovered from uninoculated control flasks, prepared 
in exactly the same way as the flasks for cultures. The flasks were 
kept in an incubator at 28° C. throughout the course of the experi- 
ment, which lasted fifteen days. 
It is obvious from Table III that these compounds of pentose 
sugars can be utilized by the fungus as sources of carbon. It is 
apparent that the yield of mycelium was less after fifteen days with 
either arabin or one of the xylans as the source of carbon than in the 
case of any one of the three sugars in twelve days. A much larger 
amount of the compound remained in the solution than in the case 
of the sugars which were removed almost quantitatively. It is evi- 
dent then that xylan and arabin are not as readily available for the 
fungus as the pentose sugars themselves. 
A comparison of xylan and arabin shows that the yield of dried 
mycelium was considerably more than twice as great from the cultures 
containing xylan, while a much higher percentage of the material was 
removed from the solution. The conclusion is obvious then from the 
table that xylan, although not as good a source of carbon as xylose, 
arabinose, or glucose is readily available and can be utilized by the 
fungus. It also seems probable that in the utilization of the xylan it 
is broken down into simpler compounds and that one or several steps 
in its digestion and assimilation is the hydrolysis of xylan to xylose, 
the sugar. If this is the case there is probably an enzyme secreted 
by the fungus which brings about this hydrolysis. 
A series of experiments was planned and carried out to see if the 
extract of the fungus was able to hydrolyze xylan to xylose under 
aseptic conditions. The fungus was grown on the mixture of nutrient 
salts already described with gum arable or glucose as a source of 
carbon. The cultures were allowed to grow about three weeks before 
the mat of mycelium was removed. It was separated from the 
culture solution, washed with a little water and ground up in a mortar. 
The resulting pulp was then placed in a flask with water and a Httle 
chloroform and allowed to stand with frequent shaking for 24 hours. 
It was then filtered and the extract used in the digestion experiments. 
The xylan was prepared by weighing small quantities, 0.2 or 0.3 g., 
into 100 cc. flasks to which 25 cc. of water was added. The mixture 
was then boiled, cooled, and 25 cc. of the extract from the fungus 
mycelium was added to each flask. The mixtures were neutral to 
