Pathogenic 3Iicrohes in the Static Condition. 47 



animals of the laboratory often rapidly leads to death 

 with suppuration or gangrene as local lesions. Wounds 

 contaminated by the soil readily become complicated 

 by accidents of the same kind. 



The specific germs which are incidentally met with 

 in the soil are those of tetanus, charbou, Pasteur's 

 septicsemia, typhoid fever, cholera, etc. 



Germs are especially abundant in the superficial 

 layers of the soil. The almost constant humidity of 

 the soil in winter carries them into the deep layers ; 

 on the other hand, during periods of drought, in 

 the absence of descending currents of water, the su- 

 perficial washing is less complete and the germs re- 

 main more in the layers in contact with the atmosphere. 

 Thus, other things being equal, the dust will be richer 

 in germs in summer than in winter. 



The micro-organisms of the soil become harmful in 

 various ways : 1st. by contaminating the vegetable 

 foods which grow upon an infected place ; 2d. by 

 distributing themselves in the air through the desicca- 

 tion of the soil ; 3d. by directly contaminating a so- 

 lution of continuity (tetanus) ; 4th. by contaminating 

 the waters which filter through the earth and which, 

 later, are to serve for alimentation. 



In the first three cases the germs must occupy the 

 surface of the arable laver : microbes which are more 

 deeply situated may return to the surface by the in- 

 crease in height of the sheet of subterranean water, 

 by the phenomenon of capillarity which constantly 

 occurs in finely divided soils, or, finally, through the 

 intermediation of earth worms, larvae, etc., a fact 

 which has been demonstrated by M. Pasteur in the 

 case of charbon. 



