ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 299 



where there is much organic debris, much exceeds that in the atmos- 

 phere, and would prevent the success of such an experiment. Ground 

 air passes easily through earth, especially through gravel and sand, so 

 that in the neighborhood of decomposing organic matter houses 

 built on such soil are liable to invasions of poisonous gases. Carbon 

 monoxide has been known to pass 20 or 30 yards through the earth 

 into a house, causing severe illness. But the worst results follow the 

 infamous practice which has been in vogue at the outskirts of large 

 towns of selling turf and gravel on building sites, allowing the exca- 

 vations to be filled in with rubbish and refuse, and building dwelling 

 houses over these sources of disease. Probably many houses in towns 

 where fever persistently breaks out owe their unwholesomeness to 

 this cause. Even where the soil is natural and undisturbed beneath 

 the foundations, there should always be a layer of impervious material, 

 such as good Portland cement or rock asphalt, between the house and 

 the ground ; or else a good space through which the outside air may 

 freely flow. Dwellings well raised above the ground escape many dan- 

 gers associated with ground air, damp, and drainage. A damp base- 

 ment is a frequent source of trouble. Hollow skirtings, casings for 

 pipes, bell wires, etc., frequently give opportunities not only to rats 

 and mice, but to deadly gases, to make their way into the apartments. 

 Inquiry is needed to discover the actual quantities of vapor "emitted 

 from different soils and subsoils, at different temperatures of air and 

 soil, at different barometric pressures, at different times of day and 

 night, and at different seasons, and at varying levels of subsoil water. 

 An examination of the different species of microbes or amoeba-like 

 organisms emitted would also be of interest. 



EMANATION OF ORGANIC PARTICLES FROM EVAPORATING- FLUIDS. 



The spread of infective organisms into the air from the surface of 

 evaporating liquids is a subject worthy of investigation. It has been 

 generally stated and assumed that an evaporating liquid contaminated 

 with impurities leaves behind it all foreign ingredients and passes into 

 the air as pure vapor. This is very far from being universally true, if 

 evaporation be understood not as a laboratory process carefully con- 

 ducted, but as a process subject to the various interferences which 

 must occur in natural conditions. Evaporation from the sea may give 

 pure vapor into the air, so long as the sea is tranquil and no bubble 

 breaks on the surface, but the breaking of waves on the ocean and on 

 the shore, and the evolution of gases from animal and vegetable life 

 and organic decay cause evaporation to be accompanied by a consider- 

 able emission of sodium chloride, and of other substances in solution, 

 into the air with the bursting of foam and bubbles and the tearing off 

 of spray by the wind. 



Marshes give off various gases, especially in the drying process, 

 besides vapor. The upward movement of the air from the drying 



