284 PROCEEDINGS OF THE INDIANA ACADEMY OF SCIENCE. 



removed, the pipette inserted and allowed to fill to the mark. The pipette 

 is withdrawn and the cubic centimeter of solution blown out into one of tht^ 

 petri dishes prepared for plating that sample. Using the same technic two 

 more one cubic centimeter aliquots are taken from the same bottle and put 

 in the other two of the triplicate plates prepared. The bottle and the pipettes 

 are put to one side. A tube of media is taken from the 40°C water bath, 

 the plug removed, the mouth of the tube flamed and the media then poured 

 into one of the petri dishes to which the aliquot of solution has been added. 

 The dish is rotated to thoroughly mix the media and solution and to get an 

 even layer all over the dish. In carrying out the above procedure as much 

 care as possible is taken to prevent the plates from being contaminated from 

 outside soiu-ces. The other two of the triplicate plates are then poured. 

 Tliree plates are then made in the same way from each of the other 1-40,000 

 bacterial dilutions and of the media. The plates are i)iled in stacks of three 

 and moved to one end of the laboratory table. The remaining thirty-six 

 petri dishes are taken from the oven, laid out on the table, labeled, and 

 platings made from the 1-400,000 bacterial dilutions. These plates are 

 stacked in piles of tlu-ee. The piles of plates after the agar has hardened are 

 inverted, placed in trays and the trays are set in the 20°C incul)ating room. 

 The plates are inverted because after they are poured they are less lial)le to 

 contamination if inverted, and because the formation of spreaders is hindered. 



Where a man works slowly or is working alone the 1-400,000 bacterial 

 dilutions are not made until after the 1-40,000 bacterial dilution luive been 

 plated. 



The jell glasses containing the one hundred gram quantities of fi(4d soil 

 are separated into three groups, one of each of the triplicate glasses from one 

 sample of soil being put in each group. To each glass of one set is added five 

 cc. of ammonium sulphate solution for nitrification tests, to each glass of 

 another set tencc. of raannite solution for nitrogen fixation tests and to each 

 glass of the third set tencc. of casein solution for aniinonification tests. The 

 jell glasses are then incubated in the 20°C incubation room for the proper 

 lengths of time. 



To each of the 10 ounce bottles containing tlu; iii'ty gram aliquots of soil 

 distilled water is added and the nitrates determined. The samples in the 

 Mason jars are analyzed, as soon as time permits, for moisture, nitrogen, and 

 other elements desired. The moisture is necessary to put results on a dry 

 basis and the nitrogen content is needed to base nitrogen fi.\ation results iii)oii. 



DISCUSSION 



Sterile Apparatus 



The technic calls for the sterilization of samplers, of dilution bottles, of 

 the glasses used for incubation tests and all other apparatus. PYom reports 

 made recently^ it would seem to some that sterility of apparatus for agri- 

 cultural bacteriology has been over-emphasized. Some might maintain that 



