APPENDIX. 365 



which arrests any solid particles. For a description of 

 the more exact apparatus employed by Maddox, Cun- 

 ningham, and Miquel reference should be made to the 

 writings of these authors, and particularly to the treatise 

 published by the last-named. 



APPENDIX D. 



EXAMINATION OF SOIL. 



SURFACE-SOIL, or mould, is exceedingly rich in bac- 

 teria. Miquel, e.g., has computed that there exists in a 

 gramme of soil an average of 750,000 germs at Mont- 

 souris, 1,300,000 in the Rue de Rennes, and 2,100,000 

 in the Rue de Monge. As agents of putrefaction and 

 fermentation they play a very important role in the 

 economy of nature, but there exist in addition bacteria 

 in the soil which are pathogenic in character. Pasteur 

 has succeeded in isolating from the earth the bacillus of 

 anthrax, and sheep, sojourning upon a plot of ground 

 where animals which have died of anthrax had been 

 buried, succumbed to the disease. Pasteur considered 

 that the spores were conveyed by worms from buried 

 beasts to the surface soil. The bacillus of malignant 

 cedema is also present in soil, and Nicolaier has culti- 

 vated a bacillus from earth which produced tetanus in 

 mice, rabbits, guinea-pigs, and other animals. 



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 

 bouillon. 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-culti- 

 vation. In another method the gelatine is liquefied in a 



