•
•
•
62 ;
Evening of the fifth day ... lactici, 7 grunthal.
Evening of the sixth day • • ... • ... 8 grunthal, 2 No. 101.
Evening of the seventh clay
• • No organisms.
Note.—Persistence of acidi lactici from start till quite late ; appearance and disappearance of lactis
æergenes ; appearance and disappearan, e of organism No. 75 ; presence of rare organism No. 6 and its
persistence for five hours at least ; finial survival of bacillus grunthal.
Besides exposing to the sunlight emulsions of fœces few experiments were
•done on some special samples of water only.
Experiment No. 35.
• The river Adyar flows close to the King Institute. It is very shallow. It is
considerably polluted all along the banks and very highly polluted just below the bridge
where many hundreds of washermen wash the clothes of the inhabitants of the city.
The water before exposure contained. 1 lactis æærogenes, 2 coscoroba, i neapolitanus,
1 cloacm 2 acidi lactici, 3 grunthal.
After 1 hour's exposure showed
... 2 lactis æærogenes, 2 cloace, 1 neapolitanus, 1
coscoroba, 3 grunthal, 1 No. 101.
2 hours'
... 3 lactis ærogenes, 6 coscoroba, 1 grunthal.
,,
g
3
lactis ærogenes, 3 No. o7, 6 grunthal.
,,
,, • • •
4 ,,
• •• 2 lactis æarogenes, 3 cloaoæ, 5 No. 67.
5
10 No. 10
,,
6
,, • • • 9 cloacæ,, 1 No. 67.
Noon of the second day (after 12 Sterile, no lactose fermenters.
hours' exposure).
Note.—The original water is very rich in different Species ; persistence of lactis æærogenes till
near the end ; appearance of organism No. 67 and particularly No. 101 late on in the exposure ; final
survival of cloaca.
Before drawing conclusions from these experiments, it is necessary to make a few
comments.
In all bacteriological work the method chosen has its own limitation ; that followed
b y u s i s n o e x c e p t i o n t o t h e r u l e . A l t h o u g h t e n c o l o n i e s , a l l o f w h i c h a r e c a r e f u l l y
'subcultured, gives a fair estimate of the organisms present in any sample, the actual
number of organisms present is an important factor. In the emulsion of faeces
used by us, at the beginning of these experiments there were from 1,000 to 1.0,000
faecal organisms per cc. Lvide table No. VIII (b) and (c)]. Obviously 10 colonies
selected from the organisms in 20 cc. of this emulsion, can only give the organisms
w h i c h p r e p o n d e r a t e n u m e r i c a l l y , t h e c h a n c e s o f i s o l a t i n g r a r e o r g a n i s m s b e i n g v e r y
.small.. But when the action of the sun has reduced the number of organisms from
10,00 per cc. to 10-100 per cc. then it is 'reasonably certain that our methods of
analysis give results which actually represent the flora of the emulsion at the time.
On the other hand 'when the organisms have been reduced to one in 50, or one in
100 cc., another error has to be reckoned with ; in the unfiltered emulsions it is common
-to get small particle of fecal matter, surrounded with an envelope of mucus, that may
contain 3 or 4 different organisms, that have, in this way, escaped the action of the rays
of the sun. Examples of this accident can be seen in our experiments. Applying these
remarks to the sunlight experiments, it is obvious that the early analyses in each case
are approximate only, whilst the later ones (as in so far as they are free from the
:second of these errors) are of very considerable value and give a more correct estimate
of the organisms present.
Now when an emulsion very rich in fecal organisms is exposed to the sun,
within the first hour or two (according to the clearness of the liquor, and the power
of the sun), a very large number of these bacilli die off, and. the more resistant
organisms begin to appear in the test portions. It must be carefully understood that
if the organisms A, B, C (A being a delicate organism, B one of medium resisting
power and. C a resistant one) be exposed to the sun, it is not maintained, that all the
A's must disappear before any of the B's begin to die, or that the whole lot of
organism B must have been killed before any of C die off. There must be a great
deal of overlapping especially among organisms whose power of resistance is nearly
equal. Again if 100 pure Cultures of A, B and C were all exposed to the sun under
similar circumstances, it is not maintained that all the A's would. die out before any
of -the B's or C's. In a' hundred such cultures, from different strains, a proportion
-of the B's might die off before all the A's were extinct, yet the conclusion to be