138 PENNINGTON: ASSIMILATION OF NITROGEN BY FUNGI 
results that have been reported by different investigators. The 
first is the old and often repeated one of experimental error. This 
reason or objection may properly be given, for it is a well known 
fact that the determination of nitrogen by the Kjeldahl method 
presents many difficulties even to those who are more or less 
expert in making such analyses. This statement will be borne 
out by an examination of the reviews and reports of controversies 
among agricultural chemists over nitrogen determinations. One 
instance may be cited. Barral reports that new block tin con- 
densers were found to absorb considerable ammonia so that accu- 
rate results could be obtained only after they had been in use a 
certain length of time. Such a source of error might cause a whole 
series of controls to show on analysis a smaller amount of nitrogen 
than a like series of experimental cultures. When the analyses of 
six similar cultures in 50 c.c. of culture medium give amounts of 
nitrogen varying from a loss of 44.9 milligrams in one flask to 
a gain of 193.6 milligrams in another, it is not safe to assume that 
free nitrogen has been fixed even although the average for the six 
cultures may be higher than the average nitrogen content for six 
controls. The results for the individual cultures should be more 
nearly uniform or there should be a reasonable explanation for the 
great differences in the nitrogen content of the different flasks. 
The objection on the ground of experimental error has added weight 
when we consider that many of these experiments have been carried 
out by persons who are amateurs in chemical analysis. 
The second reason, which does not seem to have been advanced 
as yet, is suggested by work such as has been done with Penicillium 
by Thom." It is very possible that there are some strains or 
varieties of fungi which have the ability to use nitrogen while 
many other very similar strains do not have that ability. Different 
species may have been confused and used under the same name by 
different writers. Undoubtedly several species have been used 
under the name of Penicillium glaucum, and the same may be true 
with regard to other species of fungi. With the view of obtaining 
more definite data upon this problem, experiments are now under 
way in our laboratory to obtain as many as possible distinct 
strains of fungi by cultural methods and to test them as to their 
ability to use free nitrogen. 
