i;i()(5.] 



PUBLIC IXJCUMENT — Xo. 38. 



147 



with equal amounts by weight of soil from the supi)ly bin of 

 the 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 surface ; the soil in the 

 other box Av^as untreated. One week after sterilization a 

 sample was taken from each box for the determination of the 

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

 placed on a platform scale and brought to equal weights with 

 water. Water was similarly applied every day during the 

 experiment, and the soil always contained from 17 to 20 per 

 cent, moisture. Samples 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 sann)ling the entire contents of each box 

 were thoroughh^ mixed and pulverized. 



The results of this experiment are tabulated in the accom- 

 panying table : — 



Showing the Relative Nuiaber of BactcrHa in Sterilized (Did Unsteril- 



i.:cd Loam. 



Date of taking Sample. 



Number op Bacteria per Gram 

 OP Dry Soil. 



Sterilized. 



Unsterilized. 



I90.5. 



April 3, . . . . 



April 18 



May 1, . . . . 

 May Ifi, . . . . 

 June 1 



(1,742,000 

 64,.596,000 

 66,089,000 

 •29,963,000 

 26,666,000 



.56,273,000 

 39,080,000 

 31,372,000 

 8,020,000 

 14,634,000 



The figures in this table show that steam flowing through 

 soil for half an hour not only does not kill all the bacteria 

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

 rapid mutiplication of numl^ers. 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 



