ii)(h;.] 



PUHLIO DOCUMKNT— Xo. 33. 



with equal amounts by wciglit of soil from th(( supply bin of 

 tin; station greenhouse. Before filling the boxes a (juantity 

 of soil from the bin was thoroughly mixed, and the boxes 

 filled from that, so that the soils in the two boxes were as 

 nearly alike as possible. The soil in one box was treated 

 for half an hour with flowing steam applied through per- 

 forated tubes buried beneath the surfaee ; the soil in the 

 other box was untreated. One week after sterilization a 

 sample was taken from each box for the determinalion of the 

 numbers of bacteria in the soil, after which the boxes were 

 j^laced on a platform scale and brought to equal Aveights with 

 water. AVater was similarly applied every da}^ during the 

 experiment, and the soil alwa^'S contained from 17 to 20 per 

 cent, moisture. Sanqdes for the determination of the quan- 

 titative bacterial content of these soils were taken at inter- 

 vals of about two weeks. The soil was frequently stirred, 

 and at the times of sampling the entire contents of each box 

 were thoroughly mixed and pulverized. 



The results of this experiment are tabulated in the accom- 

 })anying table : — 



Showing the Relative Number of Bacteria in Sterilized and Unsteril- 



ized Loam. 



Date op taking Sample. 



Number of Bacteria per Grau 

 OF Drt Soil,. 



Sterilized. 



Unsterilized. 



Ai)rn .3 



April IS, .... 

 May 1, . . . . 

 U:iy 18, ... . 

 .Tune 1, . 



(i,74-2,(M)() 

 (;4,.")'.H>,(M)() 

 H(i,OS',),(lO() 

 •2!),!)f!.3,(KMI 

 •2C,(!<iC,n(K» 



.5<),-27:^,0(X) 

 3!t,0.S(t,0()0 

 31,372,000 

 8,0-2!),0(M) 

 14.RS4,0OO 



The figures in this table show that steam flowing through 

 soil for half an hour not only does not kill all the l)aeteria 

 in that soil, but that it seems to act as a stimulus, causing 

 rapid mutiplication of numbers. Practically all vegetative 

 forms would be killed, but most spores would be uninjured, 

 and, given favorable conditions after treating, would germi- 

 nate. One week after sterilization the treated soil contained 



