The first experiments were made with ordinary garden earth, and they were conducted for me by Dr. Wells, of Brondesbury. These, and nearly all the subsequent experiments, were made in the same way, viz., by adding day by day what may be called a natural chance quantity of urine, varying in amount from about a quarter of a pint to two pints in the day. In these experiments, when fresh earth was used, the filtrate was always of _lower specific gravity_ than the urine added, notwithstanding the considerable evaporation which must have taken place from the surface of the filter. The total solids of the urine averaged 4·44 per cent., of which 3·45 were organic and 0·99 inorganic, while the total solids of the filtrate were 1·78 per cent., of which 1·07 were organic and 0·71 inorganic. How much of the organic and inorganic matters in the filtrate came from the mould it is not possible to say. The urea was probably all reduced, as the hypobromite method gave a percentage of only 0·15 in the filtrate, a quantity which may be disregarded in the face of the fact that the hypobromite method acts upon nitrogenous bodies other than urea. The filtrate was rather deeply pigmented, but the pigment was submitted to spectroscopic examination by Dr. McMunn, of Wolverhampton, and pronounced by him to be not of urinary origin. Further—and this is most important—the filtrate could be evaporated to dryness without offensive odour, and showed no tendency whatever to putrefy when left for months in an ordinary bottle. In short, the filtrate, although derived from urine, had none of the qualities of that fluid. The earth in the filter when stirred was distinctly ammoniacal, so that the presence of ammonia could be detected by the nose when held quite close to it, but at no time was there any foulness. When the same earth, after some months of rest, was used a second time for the filtration of urine, the same results were obtained, with the exception that the filtrate was of higher specific gravity than the urine added, and the mineral residue of the filtrate was double that of the urine. This was caused by the solution of nitrates and other soluble salts which were formed in the earth from the residue of the first instalment of urine, but the filtrate had not the properties of urine. It contained no urea, could be evaporated to dryness without offence, and showed no tendency to putrefy. In the same way, I have used deal sawdust instead of earth, and the following is the result of an analysis made for me by Dr. Kenwood in the Hygienic Laboratory at University College. July 25, 1895. _Parts per 1,000._