718 TRANSACTIONS OF SECTION I. 



directed his attention specially to the gradational changes eflFected at different 

 depths by analysing samples collected by a series of trays introduced into the 

 body of the filter at 1-foot intervals, the trays being placed obliquely from above 

 downwards, so that no tray had another in the vertical line above it. 



The plant consisted of (a) a straining-chamber of the usual type ; (b) three 

 detritus tanks of a total capacity of one-eighth the dry-weather flow ; (c) a septic 

 tank which, with the detritus tank, gave a period of quiescence of twenty-four 

 hours ; and (d) a quarter-acre percolating filter, 4 feet 6 inches deep, formed of 

 l^-inch particles of a hard, non-friable character, the septic tank effluent being 

 applied to the filter at the rate of 200 gallons per superficial yard, by means of a 

 power-driven apparatus which distributed the sewage with perfect uniformity at 

 five-minute intervals throughout the twenty-four hours. 



The following are the more important results of a series of analyses of samples 

 collected over a period of six months, the filter having been in constant use for 

 three years previously. 



The suspended solids in the tank effluent, amounting to 7"6 parts per 100,000, 

 of which 60 per cent, was mineral matter, were practically all retained in the 

 superficial layers of the filter, where the organic portion was evidently liquefied — 

 probably by aerobic organisms. Within the first foot the organic matter was 

 nearly completely oxidised, the free ammonia in parts per 100,000 being reduced 

 from 1"71 to 0'03, the albuminoid ammonia from OSi to 0'05, and the oxygen 

 absorbed from 2-18 to 32, a nitric nitrogen figure of 2 07 being recorded. It will 

 thus^be-seen that a very high-class effluent resulted from filtration through one foot 

 only, and that very little work was left for the lower strata of the filter to accom- 

 plish. The oxidation of the carbonaceous matter was also practically completed 

 at one foot depth, as is evident from the reduced oxygen-absorbed figure, as well as 

 from the fact that the carbonic acid in the air of the filter nearly reached its 

 maximum within one foot of the surface. 



A remarkable increase in the free ammonia figure in the effluent from the 

 lowest tray is recorded, and, whatever the explanation of this may be, it does not 

 arise from an accumulation of organic solids, for, on examining the filter, no such 

 accumulation could be detected ; and this was also borne out by the ascertained 

 percentage loss on ignition of the filter particles at different depths, as follows ; — 



6 inches . . 3'25 per cent. I 3 feet . . 053 per cent. 



1 foot . . 0-99 „ 4 feet . . 053 



2 feet . . 0-65 ., 1 



Possibly the phenomenon may be due to a retrograde, partially anaerobic 

 change taking place in the bottom of the filter, arising from the combustion pro- 

 ducts in the air from the work done above. 



The conclusion which the results seem to warrant is that, given fine particles 

 and good distribution, sewage filters may be constructed much shallower than 

 hitherto ; also, if a sewage, by reason of its strength, should prove to be excep- 

 sionally resistent to treatment, more will be effected by increasing the area than 

 by deepening the filter. 



2. Are the Preventive Measures which are employed against Infectious 

 Diseases Effective ? By Dr. Hime. 



3. Nitrogenous Metabolism in Normal Individuals, 

 By Dr. J. M. Hamill. 



In view of the recent experiments by Chittenden, who has shown that it is 

 possible to maintain nitrogenous equilibrium on diets containing relatively small 

 amounts of protein, it was of interest to investigate the nitrogenous metabolism 



