REPORT ON THE WORKING OF THE MICRO-BIOLOGICAL SECTION
OF THE KING INSTITUTE OF PREVENTIVE MEDICINE, GUINDY,
FOR THE YEAR 1918.
Dr.M. Kesava Pai was in charge of the Institute till the 8th January when
Dr. F. Maitland Gibson returned from leave. Dr.Gibson took over charge on
the 9th January and remained in charge for the rest of the year.
The motor-car sanctioned in G.O.No.452, Medical, dated 3rd November
1917, equipped as a travelling laboratory, and designed for visiting and collecting
clinical material from the State hospitals in Madras was received from the
vendors on the 15th January 1918. It has proved a great success.
Considerable fluctuations took place in the various kinds of examinations
made and materials prepared, but the volume of work was as large as ever.
Water analysis.— There was a considerable drop in the number of samples
examined. For the past few years the bulk of these samples were derived from
the experimental filters, but, owing to alterations in the sedimentation reser--
voirs, all work was stopped for over four months. Owing also to want of
materials required for the alteration, the mechanical filters could not be worked.
Sand filters.—The maximum reduction that could be effected in the depth
of the layer of fine sand, consistent with efficiency in filtration, formed the chief
subject of experimentation during the year. This is an important subject, as
the cost of both construction and maintenance is involved. Incidentally interest--
ing comparisons were made between the covered and the uncovered filters. In
almost all of these the covered filter proved to be considerably the better. These
are shown in tabular form in Table I.
TABLE I.
Period of arriving at the " No Lactose
fermenters in 60 c.c. " standard.
Covered filter.*
Uncovered fi l ter.*
6 days
12 days.
Period of arriving at the " No Lactose
fermenters in 1060 c.c." standard.
3 weeks.
3 weeks.
Reduction of total count—
(a) Over raw water . . .
100 fold †
80 fold.
(b) Over pre-sedimented water . . .
4 fold.
3 fold.
Lowest total count obtained per c.c. . . .
35
275
Period of running after the "1060"
standard arrived at.
58 days.
2 8 d a y s .
Maximum filtering head safely used . . .
36"
24"
* Both having a two feet layer of fine sand.
† The raw water was better at this time than when the 80 fold reduction was got with the uncovered filter. So
the superiority of the result got with the covered filter is more than is expressed by the ratio 5-4.
From this it will be seen that, with a depth of two feet of fine sand, excellent
results could be obtained. As was shown in 1917, a depth of fine sand reduced
t o 1 ' 6 " l a i d i n t h e u s u a l f a s h i o n f a i l e d , e v e n i n t h e c o v e r e d f i l t e r , t o y i e l d
satisfactory results. It was therefore decided to try a new method of supporting
the fine sand. In a filter, as ordinarily laid, the path of the water is practically
vertical and the down scour is at a maximum. If, however, during the passage
of the water through the filter, it could be made to take a zigzag and chiefly
horizontal course, it was thought that the down scour might be reduced. This
object was attained by laying country tiles, in layers bondwise, directly under the
fine sand. Spaces were left in between the tiles, but the next higher layer of
tiles covered over the spaces left between the tiles below. The spaces themselves
were filled in with coarse sand. On a first trial with this arrangement and 18
inches of fine sand above it, the results were not satisfactory. After a month the
results were irregular. This was attributed to the tiles themselves being dirty
and to the fouling of the filter by the workmen. The filter was accordingly
stopped and cleaned in the usual fashion and restarted. It was then found that
the usual good results were obtained and the "No lactose fermenters in 1060 c.c.
standard" attained to. Unfortunately the experiment could not be continued for
longevity as the alterations and additions to the tanks had to be taken in hand.
By this expedient then of the tiles, results were got, which we had failed to get
the preceding year. Experiments on these lines will be resumed.