176 BACTERIA 



matter both as nidus and as pabulum in undergoing various 

 phases of its life history. 



(d) That from food, as also from contained organic mat- 

 ter of particular soils, such micro-organism can manufacture, 

 by the chemical changes wrought therein through certain 

 of its life processes, a substance which is a virulent chemical 

 poison. 



Here, then, we have a large mass of evidence from the 

 data collected by Buchanan, Bowditch, Pettenkofer, and 

 Ballard. But much of this work was done anterior to the 

 time of the application of bacteriology to soil constitution. 

 Recently the matter has received increased attention from 

 various workers abroad, and in England from Dr. Sid- 

 ney Martin, Professor Hunter Stewart, Dr. Robertson, and 

 others. The greater part of this work we cannot here con- 

 sider. But some reference must be made to Dr. Robertson's 

 admirable researches into the growth of the bacillus of 

 typhoid in soil. By experimental inoculation of soil with 

 broth cultures, he was able to isolate the bacillus twelve 

 months after, alive and virulent. He concludes that the 

 typhoid organism is capable of growing very rapidly in cer- 

 tain soils, and under certain circumstances can survive from 

 one summer to another. The rains of spring and autumn 

 or the frosts and snows of winter do not kill them off so long 

 as there is sufficient organic pabulum. Sunlight, the bac- 

 tericidal power of which is well known, had, as would be 

 expected, no effect except upon the bacteria directly ex- 

 posed to its rays. The bacillus typhosus quickly dies out 

 in the soil of grass-covered areas. Dr. Robertson holds 

 that the chief channel of infection between typhoid-infected 

 soil and man is dust. As in tubercle and anthrax, so in 

 typhoid, dried dust or excreta containing the bacillus is the 

 vehicle of disease. 



Hitherto we have addressed ourselves to those diseases 

 the known causal organisms of which reside, normally or 



