144 BACTERIOLOGY. 



glycerine. The end of the funnel and the glass slip are enclosed 

 in an air-tight chamber, from which a small glass tube passes out 

 and is connected by india-rubber tubing with an aspirator (Fig. 73). 

 The air passing down the funnel strikes upon the glycerine, which 

 arrests any solid particles. For a full description of the apparatus 

 employed by Maddox, Cunningham, and Miquel, reference should 

 be made to the writings of these authors, and particularly to the 

 treatise published by the last-named. 



SOIL. 



Surface soil is exceedingly rich in bacteria. Miquel has com- 

 puted that there exists in a gramme of soil an average of 750,000 

 germs at Montsouris, 1,300,000 in the Rue de Rennes, and 2,100,000 

 in the Rue de Monge. As agents in putrefaction and fermenta- 

 tion they play a very important rdle in the economy of nature ; 

 but there exist in addition, bacteria in the soil which are patho- 

 genic in character. Pasteur has succeeded in isolating the bacillus 

 of anthrax from the earth. Sheep, sojourning upon a plot of 

 ground where animals with anthrax have been buried, may succumb 

 to the disease. Pasteur considered that the spores were conveyed 

 by worms from buried carcasses to the surface soil. The bacilli 

 of malignant redema and tetanus are also present in soil. Nicolaier 

 produced tetanus in mice and rabbits by inoculating a little garden 

 earth under the skin. 



To obtain a cultivation of the microbes in soil a sample of the 

 latter must be first dried and then triturated. It may then be 

 shaken up with distilled water, and from this a drop transferred to 

 sterilised broth. The employment of solid media is, however, 

 much more satisfactory : a sample of earth is collected, dried, and 

 triturated, and a small quantity sprinkled over the surface of 

 nutrient gelatine prepared for a plate-cultivation. In another 

 method the gelatine is liquefied in a test-tube, the powder added, 

 and distributed, in the usual way, throughout the medium, which 

 is then poured out upon a glass plate or made into a roll-culture. 

 In the same way the dust which settles from the air in houses and 

 hospitals, or food substances in powder, may be distributed in 

 nutrient gelatine, and examined both for aerobic and anaerobic 

 bacteria. The different kinds which develop, must be thoroughly 

 investigated as regards their morphological and biological charac- 

 ters, and pathogenic properties. 



