148 HATCH EXPERIMENT STATION. [Jan. 



nearly 7,()0(),000 bacteria per gram. This number is prob- 

 ably considerably in excess of the number in the same soil 

 immediately after sterilization, but it indicates that treating 

 soil with live steam at about 210° F. for half an hour does 

 not kill all the bacteria in that soil. The untreated soil con- 

 tained a good number of bacteria at the beginning, — about 

 56,000,000. 



During the four weeks immediately after the first samples 

 were taken there was a phenomenal increase in the number 

 of l)acteria in the sterilized soil. From 7,000,000 per gram 

 at the beginning the number had advanced to nearly 65,- 

 000,000 at the end of two weeks, and after four weeks to 

 over 66,000,000. On the other hand, the number in the un- 

 treated soil showed a steady decrease, for which no cause is 

 at present apparent. 



After six weeks the numl:>ers of bacteria in both sterilized 

 and unsterilized soils had dropped way below the numl)ers 

 found at the end of four weeks. During the next two weeks 

 the sterilized soil continued to drop oiF, though not to any 

 great extent, Avhile the unsterilized soil advanced. 



At this point it became necessary to discontinue the taking 

 of samples because of the press of other work. 



We are unable to account for the decrease in numbers of 

 bacteria in either sterilized or unsterilized soil. A similar 

 decrease in numbers of bacteria has been noted in other ex- 

 periments in the greenhouse in which unsterilized soil was 

 used. The temporary increase in numbers in tlie sterilized 

 soil may be attributed to the stimuhis given l)y the steam 

 heat ; and it appears also that sterilization had a tendency to 

 overcome, for a time at least, the antagonistic agency or 

 agencies which caused the decrease in the unsterilized soil. 



More extended experiments and observations are necessary 

 before definite conclusions can be reached res^ardinof the effect 

 of so-called sterilization on the bacterial contents of soils ; but 

 from the results obtained in this experiment and from tests 

 of other soils, both sterilized and unsterilized, we may con- 

 clude that steam treatment of soils greatly stimulates bacterial 

 development in them, and that if certain as yet unknown ad- 

 verse conditions can be removed, the high numbers may be 

 retained indefinitely. 



