254 Dr. J. M. Hobson’s Notes on 
137.—Nores on SewacGe PurIFICATION AS CARRIED out at SourH 
Norwoop Irrication Farm. 
By J. M. Hosson, M.D., B.Sc., President. 
(Read May 29th, 1897.) 
Tue purification of sewage by application to land is full of 
interest not only to the sanitarian, but to the naturalist. I now 
propose merely to sketch in broad outlines the operations, both 
mechanical and biological, which go on in this very fine sample, 
though on a comparatively small scale, of an efficient sewage 
farm. I am indebted to Mr. Thomas Walker, the Borough 
Engineer, who is also one of our members, and to Mr. Figg, the 
farm manager, for several data. 
On this farm the process is entirely one of surface irrigation, 
after removal of the coarser material by settling and screening. 
Mr. Walker has estimated that, on an average, 80 per cent. of the 
bulk of sewage water reaches the effluent, the remainder being 
absorbed by the soil and growing crops. There is about ten 
inches of soil upon brick clay. Under-drainage, which is so 
often essential in permeable subsoils, has hardly any existence 
here. 
In 1890 the sewers discharged, on an average, ‘half a million 
gallons per diem, not counting storm waters, from a population 
of 15,500; while for purifying this about one hundred acres 
were available, or about one acre to 150 inhabitants. Bailey 
Denton, in his ‘Sanitary Engineering,’ gives one acre per 
hundred of population as the normal area. But the “ proof of 
the pudding is in the eating,” and we may safely claim a good 
effluent on this farm. [In May, 1897, the estimated proportion 
was 174 per acre, but a large addition to the farm has recently 
been made, and is being utilised for irrigation.]| Weekly 
chemical tests are made of the effluent. 
I am not aware that anyone applied the bacteriological test to 
this particular farm before I did soin 1894. The bacteriological 
examination that I have attempted so far consists of two separate 
processes. The first is an enumeration of the organisms in 
measured quantities of screened sewage and of effluent, respec- 
tively ; the second is an isolation of specific organisms in the 
screened sewage and in the effluent. Both processes are full of 
interest, but my work up to the present has been very far from 
complete. 
I will not here go into the details of either process, but will, 
as I have already indicated, give you the outlines of each. 
Enumeration.—The sample taken is conveyed to the laboratory 
