1966 Journal of Applied Microscopy 



Close the slender end of the tube by holding the tip for an instant in the 

 flame. Select a point near the base of the drawn out portion of the tube and 

 heat it in as small an area as possible by directing against it the tip of a blow- 

 pipe flame. When the spot has become white hot blow strongly into the tube 

 and force the side out into a small bulb, but do not blow hard enough to burst it 

 or form a large bulb. Let this cool a minute or two, then blow air into the tube 

 and hold it imprisoned there by placing the finger tightly over the open end. 

 Direct the finest possible flame against one spot in the bulb and the imprisoned, 

 compressed air will blow out through a very minute smooth hole. The bulb and 

 the hole, if too large, may be reduced in size by heating the tube in the bunsen 

 or blowpipe flame, but care must be taken that the sides do not flow together 

 and close the opening completely. If the hole is much too large it may still be 

 made to answer by pasting over it a bit of paper in which a hole is pricked with 

 a very fine needle. 



Fit the inlet tube in the hole of the remaining piece of the rubber stopper, 

 break off the closed tip so that the gas may escape freely from it, fill the lower 

 part of the test-tube and about half of the tube e with metallic mecury, and insert 

 the slender end of the inlet tube into tube e and push the upper rubber stopper 

 into position. Carefully raise the inlet tube until its low-er end is about 5 mm. 

 above the surface of the mercury in tube e. 



The apparatus is now ready for connection with the gas supply and bunsen 

 burner. The desired temperature having been reached, any further increase is 

 prevented by sliding the inlet tube down until its tip is closed by the mercury. 



An improvement on this instrument has been occasionally introduced in the 

 form of a second tube extending through both stoppers and well into the mer- 

 cury. An iron screw or good sized iron wire can be raised or lowered into the 

 mercury, thus causing it to rise or fall in tube c, or an additional supply of mer- 

 cury can be introduced to bring that in tube c to the proper level. 

 Howard University. W. P. Hay. 



Nitrogen Fixing Bacteria.^ 



In the creation of plant food in the soil, bacteria play a very important part. 

 Of the many difi^erent organisms concerned with the formation of this plant food 

 those that gradually bring about the changes in the condition of the nitrogen 

 atoms are the most interesting as well as the most important. Just how the 

 changes occur that result in the transformation of the nitrogen of the com- 

 plex proteid molecule into that of nitrites and nitrates is not entirely clear. 

 There is also still much darkness surrounding the movement of nitrogen 

 in the soil, its change from the uncombined state in the atmosphere to the 

 combined forms in the soil. We do know that bacteria, in one way or another, 

 are directly concerned with the fixation of nitrogen. Organisms living in symbio- 

 sis with leguminous plants, and others living independently in the soil add to it 

 great quantities of nitrogen. They are the agents that help to maintain, and 

 even increase, the store of combined nitrogen in the soil. 



There are probably a half dozen organisms known today that have been 

 demonstrated to possess the power of fixing atmospheric nitrogen independently 

 of legumes. It appears, however, that such fixation takes place only in soils 

 poor in available nitrogen. Of these bacteria, there is one at least that exerts a 

 dentrifying effect in the presence of nitrates, while it makes use of free nitrogen 

 in nitrogen-poor media. There seems to be some relation between dentrifica- 

 tion and fixation ; just what this relation is has not yet been established. 



^ Abstract of paper read before the New Jersey State Microscopical Society by Mr. J. G. 

 Lipman. 



