140 BACTERIA IN THE SOIL 



which have been rescued from the oblivion of ages, and brought more 

 or less into daylight. It is but our lack of knowledge which requires 

 the present division of saprophytes, whose business and place in 

 the world is unknown. 



5. The Pathogenic Organisms found in Soil 



In addition to these saprophytes and the economic bacteria, 

 there are, as is now well known, some disease-producing bacteria 

 finding their nidus in ordinary soil. The three chief members of this 

 group are the bacillus of Tetanus, the bacillus of Quarter-Evil, and 

 the bacillus of Malignant (Edema. 



Tetanus 



The pathology of this disease has, during recent years, been 

 considerably elucidated. It was the custom to look upon it as 

 " spontaneous," and arising no one knew how ; now, however, after 

 the experiments of Sternberg and Mcolaier, the disease is known to 

 be due to a micro-organism common in the soil of certain localities, 

 existing there either as a bacillus or in a resting stage of spores. 

 Fortunately, Tetanus is comparatively rare, and one of the peculiar 

 biological characters of the bacillus is that it only grows in the 

 absence of oxygen. This fact contributed not a little to the difficulties 

 which were met with in securing its isolation. 



Tetanus occurs in man and horses most commonly, though it may 

 affect other animals. There is usually a wound, often an insignificant 

 one, which may occur in any part of the body. The popular idea 

 that a severe cut between the thumb and the index finger leads to 

 tetanus is without scientific foundation. As a matter of fact, the 

 wound is nearly always on one or other of the limbs, and becomes 

 infected simply because the limbs come more into contact with soil 

 and dust than does the trunk. It is not the locality of the wound 

 nor its size that affects the disease. A cut with a dirty knife, a gash 

 in the foot from the prong of a gardener's fork, the bite of an insect, 

 or even the prick of a thorn, have before now set up tetanus. 

 Wounds which are jagged, and occurring in absorptive tissues, are 

 those most fitted to allow the entrance of the bacillus. The wound 

 forms a local factory, so to speak, of the bacillus and its secreted 

 poisons ; the bacillus always remains in the wound, but the toxins 

 may pass throughout the body, and are especially absorbed by the 

 cells of the central nervous system, and thus give rise to the spasms 

 which characterise the disease. Suppuration generally occurs in the 

 wound, and in the pus thus produced may be found a great variety 

 of bacteria, as well as the specific agent itself. After a few days or, 



