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BACTERIOLOGICAL EXAMINATION OF SOIL. 



The collection of samples of earth from various depths 

 can be readily accomplished by means of Fraenkel's earth - 

 borer. For each culture experiment a definite quantity 

 of the soil should be weighed out, or a measured volume 

 taken. The latter is the simpler procedure, and can be 

 done with a Loffler platinum spoon (1-50 c. c.) which 

 serves the purpose of a standard volume. 



With a sterilized Loffler spoon transfer one spoonful 

 of the earth to a tube of liquid gelatin. Mix thoroughly 

 with a sterilized platinum wire and then make an Esmarch 

 roll-tube. The soil and the organisms present are thus 

 brought into perfect contact with gelatin, and after a lapse 

 of a few days colonies develop. These can be readily 

 counted, and, if necessary, with the aid of an Esmarch 

 roll-tube counter. The kind of organisms bacteria, 

 mould?, etc. can be determined by the study of the 

 colonies, and by further culture and examination. 



In this wav it is easy to determine approximately 

 the number and kind of organisms present. Unfortunately 

 this method is not adapted for the detection of anaerobic 

 bacteria which are apparently widely distributed in the 

 earth, and are represented by the well-known bacilli of 

 tetanus, malignant oedema and symptomatic anthrax. 

 These have thus far been obtained only by indirect 

 methods from the soil. Thus animals are inoculated with 

 earth, and from the tissues and organs after death the 

 bacteria are isolated. 



The surface layers of soil, to a depth of about two feet, 

 are exceedingly rich in bacteria. The number has been 

 found to vary from 100,000 to 350,000, and may even reach 

 several million, per c. c. The number rapidly decreases with 

 the depth, and at 9 to 12 feet the soil is practically sterile. 



LABORATORY WORK. Examine three samples of soil by 

 the above method. 



