BY 1?. GREtG-SMlTII. 239 



proofing is destroyed, and a freer passage is given to the diffusion 

 of the nutrients. More nutritive material is at the disposal of 

 the bacteria, and, as a consequence, thei-e is an increased growth. 



The case of sewage-sick soils appears, at first sight, to be of a 

 diflerent nature from that of ordinary soils, inasmuch as the 

 sewage itself is a nutritive solution, and decomposition will occur 

 in the sewage irrespective of the soil-particles. The sickness, 

 however, is caused by the absence of decomposition, brought 

 about by the waterlogged condition of the soil preventing the 

 sewage passing through with sufficient ease to enable the soil to 

 become aerated. 



In efficient sand-filters and sewage-soils, the particles are 

 covered with bacterial slime, and it is reasonable to suppose that, 

 in the absence of clay, the excessive formation of this slime must 

 tend to clog the filtering soil. But while the slime is growing, 

 there is a gradual deposition of fatty matter from the sc^ap of the 

 domestic sewage, and, in time, the interstices of the soil become 

 filled with a jelly of slime and fatty material, which checks the 

 free passage of the sewage. From the accumulation of fatty 

 material, sewage-sick soils should therefore be extremely sensitive 

 to the action of the volatile disinfectants or fat-solvents. 



When the sewage-sick soil is rested, the drier condition will 

 doubtless enable the bacteria to decompose the slime, l)ut the 

 mere drying may be enough to modify its gelatinous nature. I 

 have seen a slimy solution become quite limpid during evapora- 

 tion. Tt was the case of a slime obtained from a bath-sponge, 

 and, at the time, I thought that the limpidity had been caused 

 by the slime combining with the lime-salts of the tap-water which 

 had been used. A similar change may occur when sewage-sick 

 .soils are dried. Once they are thoroughly dried and moistened, 

 they certainly do not become so tough in texture as before. 



A sample of sewage-sick soil was obtained from the Metro- 

 politan Board of Water Supply and Sewerage, by favour of the 

 Medical Officer, Dr. E. S. Stokes. The soil had originally been 

 a shelly sand such as is found upon the shores of Port Jackson, 

 and, in the sample, the original nature of the filter-bed was 

 clearly seen. The sewage had come from the residential suburb 



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