1912] Lipman : Bacteria in Soils of Arid Regions 3 



successive sterilization of the auger (before taking each sample), 

 to obtain a sample which represented, uncontaminated, each of 

 the soils as they are found in their natural state in the field. 

 With a sterile spatula there were taken from the samples thus 

 obtained with the auger representative samples which were im- 

 mediately placed in sterile cotton-stoppered bottles. It was 

 soon found, however, that this method could not be relied upon 

 for accurate results, since no matter how carefully the samples 

 were thus taken, there were many chances for contaminating 

 samples from the lower layers with soil from the upper layers 

 and thus obtaining results which were erroneous. After much 

 experimenting we finally decided on the following plan for 

 taking the soil samples, which, so far as I know, is as free from 

 chances of error as any method that can be adopted in a series 

 of investigations which must of necessity be so extensive. In- 

 deed, I believe the chances for error here are so small that they 

 cannot affect the validity, to any appreciable extent, of the 

 results obtained. Our method consists in having dug, a day 

 or two prior to sampling, a hole twelve feet in depth with at least 

 one vertical wall and large enough for a man to stand in. The 

 samples are taken as follows : With a sterilized spade, a layer 

 of soil of about five or six inches in depth is sliced down along 

 the whole length of the wall which is to be sampled. After this 

 is done, to remove the soil that in the one or two days' exposure 

 may have become contaminated, the fresh surface thus obtained 

 on the vertical wall is sterilized hy means of a plumber's torch 

 on the surface surrounding every spot, previously marked off, 

 at which a sample from each foot in depth is to be taken. When 

 this is done a sterile cylindrical tin tube, a little over one inch 

 in diameter and about ten inches long, is driven at right angles 

 to the wall into the spot selected for sampling, immediately 

 drawn out when sufficient soil has thus been obtained, and the 

 cotton plug replaced. In our first experiments, glass tubes of 

 the size described were employed, with paraffined corks at one 

 end and cotton stoppers at the other. We found this to be a 

 poor method, however, and have replaced the glass by tin tubes, 

 closed at one end and plugged with cotton at the other. These 

 are sterilized at 150 degrees centigrade for one hour and a half 



