318 Professor Frank Clowes [March 9, 



These typical researches render it evident that the organisms and 

 their spores, which are produced at or near the earth's surface, are 

 wafted by natural atmospheric movements to some height, but are 

 constantly tending to subside, and to sow the organisms broadcast as 

 they descend. 



It has been shown by more recent bacteriological investigations 

 that many of these minute organisms are normally present in the 

 living organism, and make their appearance in large numbers in the 

 dejecta. It is therefore not remarkable that sewage, which contains 

 the dejecta of men and animals, as well as the washings of consider- 

 able road and other surfaces, should contain micro-organisms and 

 their spores in large number. 



The fact that animal dejecta and sewage are inoffensively and 

 gradually resolved into simple chemical compounds by contact with 

 different kinds of soil has long been known, but this resolution has, 

 until recently, been attributed to the purifying action of the earth 

 itself, or of the organisms which it may contain. It is now abundantly 

 proved that the resolving or purifying agents are, in the main, the 

 micro-organisms which were originally present in the dejecta them- 

 selves, although undoubtedly organisms derived from the air, and 

 those already present in the soil, contribute to the change when they 

 are present. 



The experimental purification of sewage by letting it stand in 

 tanks filled with flints, gravel, coal, coke or other mineral substances, 

 proves that there is no special virtue in soil. These experiments, 

 originally commenced by the State Board of Health, Massachusetts, 

 in 1887, have been repeated by many public sanitary authorities, and 

 the results have been abundantly verified ; and in various localities 

 broken stone, broken slate, broken clay vessels, " ballast," or burnt 

 clay have been successfully employed in the tanks in place of the 

 materials which were originally used. 



For the successful and inoffensive treatment of sewage by this 

 means, a preliminary " priming " of the material is necessary. This 

 is effected by allowing it to remain immersed in sewage for several 

 hours daily for a few weeks. Sewage, which is then introduced and 

 allowed to remain for a few hours in the tank containing the 

 "primed" coke or other material, has the amount of its putrescible 

 dissolved matters considerably and rapidly reduced, while its solid, 

 finely-divided fzecal matter is brought into solution, and caused to 

 undergo, in large measure, resolution into simple inoffensive com- 

 pounds. 



In order that these changes may be completed inoffensively, it is 

 necessary that the " primed " coke surfaces shall be frequently placed 

 in contact with air, and the process is therefore an intermittent one. 

 The coke-bed is first filled with sewage, which is then allowed to 

 flow out from the bottom and to draw air into the interstices of the 

 coke. After the coke surfaces have been for several hours in contact 

 with the air, the cycle of processes is repeated. The treatment of 



