1919] 



ALLEN AZOTOBACTER CIIROOCOCCUM 



19 



of a suspension prepared as described above from a 24-hour- 

 old streak of the F 2 generation on Ashby's soil extract agar. 

 The " micro" cultures were kept in an incubator at 30-31° C. 

 for two weeks and then ar alyzed for total nitrogen according 

 to the procedure described above except that 15 cc. concen- 

 trated H2SO4, 7 gms. Na2SC>4, and 2 cc. 10 per cent CUSO4 were 

 used for each digestion. As the amount of mannite was only 

 one-tenth that in the previously described experiments, di- 

 gestion was completed in much less time. It was, however, 

 not to be designated as rapid or free from the annoyance of 

 foaming. In fact, from 3 to 5 hours were required for the 

 digestion mixtures to clear, and some cultures were lost as a 

 result of foaming out of the digestion flasks. 



The results are reported in table iv. The data on fixation 

 are computed to mgs. per 100 cc, i. e., 10 times the amount 

 actually observed. 



TABLE IV 



FIXATION OF NITROGEN BY AZOTOBACTER CHROOCOCCUM IN MODIFIED 



ASHBY'S SOLUTION 





Addition to culture 



medium 



Treat- 

 ment 



No CaCO, 



CaCO 



1 added 



No. 



N 

 found 



per 



culture 



(mgs.) 



N 



fixed 



per 



100 cc. 



(mgs.) 



N 

 found 



per 

 culture 

 (mgs.) 



N 



fixed 



per 



100 cc. 



(mgs.) 



25 



Control 



Sterile 



Inoc. 



Inoc. 



Sterile 



Inoc. 



Inoc. 



Sterile 



Inoc. 



Inoc. 



Sterile 



Inoc. 



Inoc. 



Sterile 



Inoc. 



Inoc. 



Sterile 



[noc. 



[noc. 



.360 

 .544 : 

 .487 



.329 

 .646 

 .601 



.227 

 .351 

 Lost 



Lost 

 .756 

 .674 



.196 

 .334 

 .326 



.210 

 .734 

 .615 



1.84 

 1.27 



3.17 

 2.72 



1.24 



5.29* 

 4.47* 



1.38 

 1.30 



5.24 

 4.05 1 



.439 

 .660 

 .660 



.453 



1.357 



.850 



.190 



.422 

 .448 



.133 

 .955 

 .949 



.234 

 Lost 

 .521 



.215 

 .997 

 .906 





26 



Control 



2.21 



27 



28 

 29 



Control 



0.01 mg. Fe 2 0, 



0.01 mg. Fe*O s 



2.2, 



9.04 



30 



31 



32 



0.01 mg. Fe^Os 



Control 



Control 



3.97 



2.32 



33 



Control 



2.58 



34 



0.05 mg. Fe 2 3 



^^m ^* ^^ r 



35 



0.05 me. FeiOi 



8.22 



36 



0.05 me. Fe 2 Oi 



8.16 



37 



Control 



^ta^ • «• ^^r 



38 



Control 





39 



Control 



2.87 



40 

 41 



42 1 



0.10 mg. Fe 2 Oa 



0.10 mg. Fe 2 8 



0.10 mg. Fe*Oi | 



7.82 

 6.91 



* Computed from No. 31 as blank. 



