280 A MANUAL OF BACTERIOLOGY 



microbes than sub-soil; and at a depth of 8 or 

 10 feet there are hardly any present. (4) Most of 

 the microbes of soil are harmless when introduced 

 into the human or animal body ; but the bacilli of 

 tetanus, anthrax, 1 typhoid fever, malaria, and 

 cholera have been found in soil. 



Dowd's investigations have proved that the ex- 

 posure of so much soil in the upturning of streets 

 is detrimental to the health of the surrounding 

 community. However, it should be remembered 

 that so long as the soil is wet it cannot spread the 

 microbes in the air; but the soil does not long 

 remain wet. It dries beside the trenches, it adheres 

 to the implements, the clothes and boots of the 

 workmen, and, in fact, to everything which comes 

 in contact with the trenches ; and, finally, much of 

 it is left on the surface when the pavement is relaid. 

 In all these conditions it may be carried away as 

 dust. The microbes go with the dust, and access 

 to the body is then made easy. The amount of 

 dust in the air is much increased by these trenches ; 

 but, on the other hand, the deeper layers of soil or 

 earth from which this dust is derived do not contain 

 nearly so many microbes as the surface layer. 



An important method for dealing with the dust 

 of streets, especially during epidemics, is to water 

 them with some germicidal substance, by means of 

 the Strawsonizer or pneumatic distributor. 2 This 

 machine is capable of distributing one or more 



1 Pasteur in Bulletin de VAcademie de Medecine, 1880. 



2 Obtainable at Messrs. Strawson and Co., Newbury, Berk- 

 shire. 



