136 PENNINGTON: ASSIMILATION OF NITROGEN BY FUNGI 
In general, the method has been to grow pure cultures of the 
fungus in 100 c.c. of the solution in one-liter flasks. These flasks 
were arranged in a series with wash bottles of sulfuric acid and 
potassium hydroxid and connected by tubes through their rubber 
stoppers in such a way that air, freed from all combined nitrogen 
in the form of ammonia and oxids of nitrogen, could be drawn 
through the flasks by means of a filter pump. Controls were 
always used, some consisting of 100 c.c. of the medium without 
the fungus, others of cultures of the fungus in the medium to 
which enough combined nitrogen had been added to insure a 
good growth of the fungus. At the conclusion of the growing 
period chemical analyses were made of the cultures and controls 
to determine the mount of combined nitrogen in each. 
In the chemical analyses different modifications of the Kjeldahl 
method were used. If it was certain that no nitrate was present, 
Gunning’s modification was found to be the most satisfactory; 
if nitrates were present, the Gunning-Jodlbauer modification was 
used. When very small quantities of nitrogen were to be deter- 
mined, as in the culture media in which no combined nitrogen 
has been put or in a very small fungus felt, the digestion was 
carried out in the usual way, made alkaline, then distilled and the 
distillate caught in a volumetric flask containing a small amount 
of dilute hydrochloric acid. The amount of ammonia was then 
determined by the colorometric method in which Nessler’s reagent 
and Nessler’s comparison tubes were used. When the amount of 
nitrogen was about 0.5 milligram or less, this method was found 
to be more satisfactory than the ordinary method by titration. 
There is also no danger of error by the carrying over of small 
amounts of the fixed alkali, during the distillation, for they would 
make little if any difference in the color. 
In all cultures in which dextrose was used there was some 
growth. In the first series the titration method was used and the 
total nitrogen content of the several flasks was found to be 0.44— 
0.62 milligram. A blank with one gram of dextrose gave 0.42 
milligram of nitrogen. In the next series, the colorometric method 
was used and all analyses of blanks and cultures in which cane 
sugar, glycerine, and potassium tartrate were used gave amounts 
of nitrogen between 0.30 and 0.37 milligram. At the same time 
