58 



RACTERIA IN RELATION TO PLANT DISEASES. 



precautions has led to the statement that certain strict aerobes are able to grow on 

 ordinary media in the absence of oxj'gen, and that anaerobes are ver)' uncertain in 

 their behavior on standard media. Old pj-rogallic acid should be avoided and some 

 preliminary experiments should be made as to the rapidity of the absorption of the 



oxygen from a given space before the 



organism is tested. The writer found 

 one brand of pj-rogallol which re- 

 moved the oxygen from a small space 

 in six hours, another required about 

 eighteen hours, a third required sev- 

 eral days (time enough for a strictly 

 aerobic organism to make a visible 

 growth). Leaks may be detected read- 

 ily by including with the cultures 

 a fermentation-tube, the inclosed arm 

 filled with water except for a small 

 bubble of air. On absorption of the 

 oxygen this bubble expands to a 

 diameter which should remain con- 

 stant if the jar continues air-tight. 



The gas remaining in receptacles 

 from which the oxygen has been 

 removed by the potash - pyrogallol 

 method is not pure nitrogen, but 

 nitrogen plus a variable small amount 

 of carbon monoxide, which is said 

 to be most abundant when the ox)'- 

 gen is absorbed slowly. This small 

 amount of CO is harmless to many 

 bacteria, but the writer has some 

 reason for suspecting that it is inju- 



Fig. 54.' 



rious to others, even if it does not entirely inhibit growth. 



The writer has found the following contrivance (fig. 55) a ver}' simple one for 

 testing the ability of organisms to grow in nitrogen : A U-tube of thick, clear glass, 

 with arms about 10 to 12 inches long, open at the ends and having a uniform inside 

 diameter of about i inch, serves as the culture-chamber and gas-receptacle. Two 

 short, rimless, cotton-plugged test-tubes containing the media to be tested are inocu- 

 lated and thrust one above the other into one arm of the U-tube, into which is then 



*FiG, 54. — Novy jar of large size for Petri dishes and numerous test-tube cultures. Clamped 

 as when in use. Between ,the clamped parts is a rubber gasket, carefully waxed and vaselined. 

 Darwin's wa.x -mixture is advised. The writer also usually wires in flhe iwaxed top parts. The gas 

 inflow is cut off by twisting the uppermost (horizontal) ground-glass stopper, which must be care- 

 fully vaselined. One-third actual size. 



