302 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 



The floors and walls of rooms must often be very suitable culture 

 grounds for the microbes of disease. Many fungi grow upon danip 

 plaster, damp wall paper, the interstices of floors, and upon rough sur- 

 faces and ledges in empty and also in occupied rooms. The Clicetonivm 

 chartatum, for example, develops on paper and on the binding and 

 insides of books wherever they are near a damp wall. Paper and size 

 are well adapted to the settlement and multiplication of molds and 

 probably also of some pathogenic microbes. 



Bricks, mortar, plaster, and paper are all highly porous, and admit 

 the passage of air continually through them. A common brick can 

 absorb a pound of water, and plaster is also hygroscopic. We have, 

 then, this condition in a room, that it is surrounded by damp, porous 

 material, largely contaminated with organic dust and gases from the 

 interior condensed within the walls and in the flooring or carpets. 

 The resemblance to porous, damp, contaminated ground which is a 

 known source of disease, is sufficiently close to make it highly desir- 

 able that better provision should be made (1) against damp in walls, 

 (2) against the penetration of organic vapors and dust into the material 

 of walls and into the interstices of floors, and (3) for the easy cleaning 

 of walls with soap and water, and of floors which should be without 

 interstices, by dry rubbing or with paraffin or otherwise. 



AERATION AND SELF-PURIFICATION OF RIVERS. 



The oxygen of the air contained in water has been supposed to play 

 an important part in getting rid of the contamination of organic sub- 

 stances and in diminishing the number of pathogenic microbes in the 

 water of streams used for drinking. A large number of experiments 

 have been made in different countries with the object of determining 

 the degree of safety with which water may be used for imblic supply 

 which has run in the open air for various distances after contamina- 

 tion with sewage and other impurities. 



The investigation is by no means a simple problem, and where the 

 bacteria are found to have greatly diminished in number in the course 

 of a few miles, the result is often due to other influences besides aera- 

 tion, of which gradual dying out of the organisms is one, and sedimen- 

 tation commonly the most efficient. Frank's experiments on the River 

 Spree, at Berlin, showed that, though in flowing through the city, the 

 river contained hundreds of thousands of bacteria in the cubic centi- 

 meter, the water some miles lower contained only 3,000 to 8,000, about 

 the same number as in its upper course. In the Isar, below Munich, 

 the number fell from lo,231 to 2,378 in the course of 22 miles. In the 

 Thames and the Ure, Franklaud did not find any considerable diminu- 

 tion. The Massachusetts State Board of Health found in the course of 

 23 miles a diminution of free ammonia from 1,728 to 1,299, of albumi- 

 noid ammonia from 826 to 382, of total nitrogen from 3,000 to 2,156, and 



