^^ 



174 OUTLINES OF BACTERIOLOGY 



this microbe, it was found that after twenty days 53'6 milligrams of 

 nitrogen had been taken from the atmosphere. In this particular 

 experiment 40 grams of dextrose were present in the nutrient solution. 

 At the close of the experiment all of this had disappeared, and its place 

 had been taken by acetic and normal butyric acids, and traces of alcohol 

 and lactic acid. 



Beyrinck's brilliant researches also showed that Clostridium Pastori- 

 anum was not the only organism capable of assimilating the free 

 nitrogen of the atmosphere. 



By changing the form of the carbon supply in his nutrient solution, 

 using, for example, mannite instead of dextrose, he was able to isolate 

 from the soil two other similar organisms, which he named Azotobacter 

 ohroococcum and Azotobacter agilis respectively. These were found 

 capable of assimilating the atmospheric nitrogen only when acting in 

 symbiosis with other organisms. The genus Azotobacter is remarkable 

 for the size of its cells, which resemble yeast 

 more than bacteria cells. The general appear- 

 ance of the individuals of this genus is given 

 in Fig. 108. They appear as Diplococci or 

 short rods 4-6 /j, thick, have vacuolated con- 

 tents, and shiny walls. They also possess short 

 polar cilia, and are consequently normally 

 motile. Judging from their shape, size, and 

 Fig. los.— Azotobacter. general characteristics, it is still doubtful 

 whether the genus Azotobacter should not be 

 included among the lower Algae rather than in the Baoteriaceae. 

 With regard to the Fungi, the following have been credited with 

 possessing the power of assimilating free nitrogen from the atmo- 

 sphere : Aspergillus niger, AUernaria tenuis, Gymnoascus, Penicillium 

 glaucuni, Mucm- stolonifer, Endococcus furpurascens, Phoma betae. In 

 most of these the amount of nitrogen gained was from 1 to 2 mgr. 

 in a 50 c.c. nutrient solution. In Phoma betae, however, as much as 

 10"5 mgr. was obtained from the same quantity of nutrient solution. 

 Unfortunately these results have not been fully confirmed, though they 

 are probably correct. One subsequent research gave negative results, 

 but it is possible that the Fungi do not always assimilate free nitrogen, 

 but do so only when a certain set of conditions hold, so that we 

 cannot throw over the positive results, but can only hold back our 

 judgment till the results of further researches are forthcoming — a 

 precaution which is rendered necessary when we remember how easily 

 the physiological properties of bacteria can change. 



