100 ABSTRACTS 



In conclusion it would seem from the experiments above cited that the 

 protozoa do not have a detrimental effect on the processes of ammoni- 

 fication, nitrification and free nitrogen fixation in the soil. 



A Study of the Nodule-Forming Bacteria. F. O. Ockerblad. 



This paper deals with the relative longevity of Ps. radicicola (twelve 

 strains from the more common legumes) in sealed and unsealed culture 

 bottles such as are used for distribution of nodule-forming bacteria. 

 The media used are a liquid medium (1000 cc. ash leachings from 5 

 grams wood ashes plus 1 per cent saccharose) and a solid medium (same 

 as above plus 1 per cent agar). 



In preparation all bottles were inoculated and incubated at room 

 temperature (20°-22°C.) for two weeks, then half the number of each 

 of the solid and liquid cultures of the different strains were sealed by 

 removing the cotton plug and inserting cork stoppers which had been 

 soaked in mercuric chlorid 1: 1000 and flamed at time of insertion. At 

 10-day intervals a culture of each strain on both the solid and liquid 

 media is analyzed by plating in ash agar to enumerate the number of 

 living cells and by making direct count with Thoma counting chamber 

 for total numbers, dead and alive. 



The bacteria in the liquid cultures both the sealed and unsealed 

 are dying quite rapidlj'-, with the greatest rapidity in the sealed cultures. 

 On the solid medium the number of living cells in the sealed cultures is 

 decreasing, approximately 25 per cent in 20 days; while the unsealed 

 are showing little or no decrease. The total number of bacteria on the 

 solid medium is greater than in the liquid culture media. 



If we may be permitted to draw conclusions from limited and in- 

 complete data we should say that a liquid medium for the distribution 

 of nodule-forming bacteria is unsuitable because of the small total 

 number and of a high mortality; and that the deterioration of cul- 

 tures on solid medium in sealed form should be recognized. 



Quantitative Media for the Estimation of Bacteria in Soils. R. C. Cook. 



Comparative tests of several different media upon twenty soils are 

 reported. 



The length of incubation period and manner of sterilization were 

 incidentally studied as affecting the comparative values of the respec- 

 tive media with the indication that five days is of sufficient duration to 

 secure satisfactory counts. 



Lipman and Brown's modified synthetic agar. Temple's peptone 

 agar. Brown's albumen agar, and Conn's sodium asparaginate agar 

 were compared with several other agar media having varied sources 

 of nitrogen. 



Highest counts were obtained quite consistently with the sodium 

 asparaginate agar during the first part of the work. Later a medium 

 was developed in which ammonium nitrate and urea were employed; 

 this gave results fully as good as any other in a limited number of tests. 

 Albumen agar in which the albumen was dissolved in sodium hydroxide 



