390 



CLINICAL BACTERIOLOGY. 



tion of the sample. To this end mortar and pestle are 

 sterilized, and one gram of earth diluted with ten times the 

 amount of sterile 0.6 per cent, solution of sodium chlorid is 

 rubbed up. By means of a graduated platinum spiral a 

 definite amount is removed, and with this gelatin-tubes 

 (with three or four dilutions) are made in the usual man- 

 ner. 



In order to obtain deeper layers of earth a special boring 

 instrument (Fig. 84), devised by C. Frankel, is employed ; 

 this can be opened at the desired depth by a rotatory 

 movement, and, when it is rilled, is again 

 closed and removed. 



By these methods, however, informa- 

 tion is gained only with regard to the 

 aerobic bacteria present in the earth. 

 As, however, anaerobic microorganisms 

 occur in the soil, especially in manured 

 garden-earth, in not inconsiderable num- 

 ber, it is advisable in making bacterio- 

 logic examinations of earth always to 

 prepare also anaerobic plates. If it be 

 desired to isolate a certain bacterium 

 from the earth, animal experimentation 

 is resorted to if the organism is patho- 

 genic. If the bacterium sought pos- 

 sesses resistant permanent forms, the 

 sample of earth may be distributed in 

 water and heated for a considerable 

 length of time to between 80 C. (176 

 F.) and 90 C. (194 F.), and then plates 

 are made. 



The Bacteria of the Soil. The superficial layers of 

 earth, even when uncultivated, contain large numbers of 

 bacteria about 100,000 to the cubic centimeter, and more. 

 The further progress is made in depth the smaller the 

 number of bacteria present in earth, and unless coarse 

 gravel be present, germs will no longer be found at a depth 

 of between ^ and I ^ meters, thus at the ground-water 

 area. Porous soil filters the air, as well as liquids, in a 

 perfectly reliable manner. This is naturally not the case 

 in regions where fissures and breaks of any origin are 

 present. 



Bacilli especially are found in earth. Of innocuous mi- 



Fig. 84. Frank el's 

 instrument for obtain- 

 ing earth from various 

 depths for bacteriologic 

 study. 



