106 



L. T. SHARP 



One cubic centimeter of the various dilutions was plated with 

 synthetic agar made up as follows: 0.2 gram MgS04, 0.5 gram 

 K2HPO4 neutralized with NaOH, 0.05 gram peptone, 10 grams 

 dextrose, and 20 grams of agar in 1000 cc. of tap water. The 

 plates were incubated at 28°C. for five days before the first 

 count, and subsequent counts were made. The results recorded 

 are as follows: 



In alkali soils Nos. 1 and 2 we find comparatively few organ- 

 isms, probably owing to the small number originally present. 



TABLE 1 



NO. OF SOIL 



NTTMBER OF MOLDS AND BACTERIA PES GRAM 



Molds 



Bacteria 



Total 



1 



00 



5,000 



5,000 



2 



00 



60,000 



60,000 



3 



00 



250,000 



250,000 



4 



10,000 



90,000 



100,000 



5 



00 



75,000 



75,000 



6 



40,000 



380,000 



420,000 



7 



150,000 



380,000 



530,000 



8 



90,000 



480,000 



570,000 



9 



10,000 



550,000 



560,000 



because of the toxicity^^ of the alkali salts. Perchance the in- 

 crease in concentration of the hygroscopic film through drying 

 brought about plasmolysis. The number of molds in soils 6 and 

 7 is particularly noticeable, due to the resistance of mold spores 

 and also to the prevalence of molds in the hea\'y soils of the 

 Stockton region, which are well supplied with organic matter. 

 Soil No. 8, though a sandy loam, harbors 90,000 molds per gram. 

 The number of organisms in normal soils Nos. 3, 4, 5, 6, 7, 8, 

 and 9, varies from 75,000 to 570,000. It is quite conceivable that 

 these amounts are perhaps one-fifth of the original number, 

 which would necessitate a count of from 350,000 to 2,850,000 

 per gram. Fresh samples of soils have differed from these numer- 

 ical limits in both directions. Soils Nos. 4 and 5 with the smallest 

 count are sub-soils of heavy adobe soil, which retains about 

 two and a half times as many organisms as the samples taken 



" Centblt. f. Bakt. 33: 55. 1912, and 33: 313. 1912. 



