EXPERIMENT STATION BULLETINS. 469 



The data concerning ammonia production in quartz sand are sum- 

 marized in Table VIT. Tliis table corresponds to Table TTT jiiul il 

 lustrates as plainly as can be desired, the reason why the soil solution 

 has been chosen for a basis. From Table III, it was concluded that 

 the optimum moisture for anmionia formation in quartz sand is 20%, 

 that the decomposition at 5% was negligible and that the peptone so- 

 lution equaled, in its suitability for li. mycoidcs, the sand with 10% 

 moisture. These conclusions must be revised, because they have been 

 drawn without regard to the most vital needs of microorganisms, name- 

 ly the moisture. While Table III says that the ''soil" produces most 

 ammonia at 20% moisture, Table VII shows that the "bacteria" grow 

 best at 10% moisture. While Table III indicates that the soil with 

 10% moisture produces about as much ammonia as the solution, Table 

 VII demonstrates that the bacteria in the soil with 10% moisture de- 

 velop about 8 to 9 times as fast as they do in solution. 



These two sets of data are not contradictory. Table III represents 

 the standpoint of the farmer who wants the product regardless of 

 where it comes from. Table VII represents the view point of the 

 scientist who wants to study the conditions of existence in the soil. 

 The results become contradictory only if conclusions are drawn with- 

 out due regard to the points emphasized. The fact that 100 g. of sand 

 + 20 cc. of water produce more ammonia than 100 g. of sand + 10 

 cc. of water, does not allow the conclusion that the bacteria grow 

 better in sand -f 20% moisture. Table VII shows that the opposite 

 is the case. But this last statement does not interest the farmer; he 

 wants the largest amount possible in his soil, not in his soil solution. 

 The only possible way of studving life conditions in soil is, of course, 

 .that of Table VII. 



The sand cultures show an increase of .318 to 823% over the solu- 

 tions which is due entirely to the physical qualities of the sand, all 

 chemical factors being excluded. The soils show less ammonia forma- 

 tion than the sand cultures. If we compile the largest amount of am- 

 monia formed in each soil the following data are obtained: 



Surface soil, 160 mg. Peat 24 mg. 



Subsoil, 120 " Sand 238 " 



Soil A, 224 " Solution 23 " 



Soil B, 179 " 



These data should be compared with those on page 21. Here again, 

 the contrast of the two viewpoints is very striking. The best medium 

 for B. mycoides is evidently the sand, where it produced 10 times as 

 much ammonia as in the solution. The peat is such an inadequate 

 medium for B. mycoides, so much inferior even to the subsoil that one 

 is led to believe in some antiseptic property of peat. The physical soil 

 properties of peat, especially as far as ventilation is concerned, are 



