BACTERIA IN NATURAL PROCESSES 69 



teria in any portion of the soil ; many of them are anaerobes and 

 many require special media for their growth. Of such as can be 

 grown on ordinary media there have been found approximately 

 100,000 per gram in an uncultivated soil, 1,500,000 per gram in 

 a garden soil, and 115,000,000 per gram in soil mixed with sewage. 

 The actual numbers, must be infinitely greater. 



Bacteriological Examination. For the examination of sur- 

 face soil a specimen may be taken with a sterile spoon or tube. 

 When taken from a lower level a special instrument is generally 

 used. The usual form is that of a drill with a hollow chamber 

 just above the point. A sliding door to the chamber is so arranged 

 that it can be opened or closed by a mechanism controlled at the 

 handle. The chamber is first sterilized and then the drill is forced 

 into the ground to the desired depth ; the door of the chamber is 

 opened and by a twisting movement the soil is forced into the 

 chamber ; the door is then closed and the drill removed. 



Before' removing the soil the chamber is weighed, then a small 

 amount about the size of a bean is dropped into a flask containing 

 a liter of sterile water and the chamber is again weighed to ascer- 

 tain the quantity removed. The moisture in the flask is then 

 vigorously shaken to insure an even distribution of the organisms, 

 and the examination is made in the same manner as that described 

 for water. Quantities as small as 0.1 c.c. and 1 c.c. should be 

 plated and cultivated both aerobically and anaerobically. 



Almost all the bacteria in the soil are saprophytes. The or- 

 ganisms pathogenic for man do not find conditions favorable 

 for development ; for the most part the temperature is too low, and, 

 further, they are so crowded out by the saprophytes that they die 

 in the struggle for existence. 



Pathogenic Bacteria Associated with the Soil. Tetanus bacilli. 

 Spores of the tetanus bacilli frequently occur in the soil, al- 

 though it is improbable that the organisms ever multiply there. 

 Wound infections usually occur as a result of contact with the soil 

 of the object inflicting the wound. 



Anthrax Bacillus. The anthrax bacillus, like that producing 

 tetanus, would probably not continue to exist in the soil were it 



